Zed Head

Your wheel bearngs are loose. Even though there is a somewhat complex process for setting tapered wheel bearing preload, you can get really close just by tightening them by hand. Pop that cap off and turn the nut until it's hand tight. Your aftermarket lugs are so long it wouldn't be a surprise if they were bottoming out in the nut. That rust and corrosion on the hub should not be there, where the nut is supposed to be clamping the wheel down. That's a sign that the wheel is not seating on the hub.

I was trying to point at where the noise might be coming from. Your description, with the video of twisting the propeller shaft, implies a sort of rotating clunking noise. A bad u-joint in one of the half shafts could cause that. Another possibility is the transmission mount. You can get under the car and lift up by hand on both the tail of the transmission and the nose of the differntial. Both have a lot of leverage available. Get under there and move things around. Use a long screwdriver in the u-joint yokes to see if they're loose. They're tough, they handle lots of torque. Many possible causes.

Looks good and it will probably help you in the future. You need a column with results though. More detail too, like brand of injector, etc. Maybe even cost but you can keep that private. I had a spreadsheet for a while for my car. Realized the nickels and dimes had added up in to the thousands for the whole car as a project. $20 here, $50 there. Doesn't take long. Don't look if you think your hobby is inexpensive. It's probably not.

So it looks like a pretty good option. For a premium of $20.99 (in my case), 18%, a person gets the peace of mind of a brand new starter. WAI shipped to my place from Rockauto would cost $135.98. $11.99 Fedex ground. Driving to O'Reilly Auto for their only option, remanufactured, would cost $114.99. My hobbay was making the old stuff work but if I wanted dependability I'd go with the WAI, I think. Probably their alternator also.

The other two drive shafts. Sometimes called half shafts

Your diff mount looks in pretty bad shape. But it usually causes a clunk when shifting, not a constant noise while coasting. The play in the driveshaft (propeller shaft) is normal for the diff, if the tranmsission is in neutral. Can't tell if the diff gears are stopping the movement or the transmission. Don't forget the other two drive shafts. Four more u-joints.

https://www.classiczcars.com/settings/signature/

You mean "are there are more than the three screws across the top edge?". Here's a 240Z.

Not 100%, but typically there are hook-like devices to hold one side and the screws lock it in so that it can't come out of the hooks. Not sure what exactly you're trying to fit. But here are some things that look like they might be involved. Modified your picture. I went to BAT to try to find an example and found that people are doing all kinds of different things. Might be worth browsing aorund to get some ideas. Many people just use the four screw holes, apparently. Naked plate. https://bringatrailer.com/datsun/280z/?q=280z Some only have two holes and the bottom hooks.

This might affect starting but won't affect running. It's usually caused by a bad check valve in the pump or a leaking regulator. This could be caused by many things. Sometimes you just have to make a check list and run through the tests in the FSM or the Fuel Injection Book. TVS, AFM, ignition timing, clogged injectors, clogged muffler (not actually one of the tests), clogged converter (same), rotten EGR channel, and more, could be a cause. But without seeing all of the things that are correct it's impossible to make a good guess. This is page 6. If you made a file, like in Wordpad, or a Google spreadsheet and linked it so that people could see your test results easily, they could zero in on next steps. You could zip tie those injector clips on temporarily.

The carparts site is back up. It has some stuff. Looks like the parts taken out were half right. https://www.carpartsmanual.com/datsun/Z-1969-1978/electrical/starter-motor/for-manual/to-sep-75

That test sheet is impressive. The mounting flange looks thick. Not a bad thing but I wonder if the bolts/screws are long enough. Might just be the pictures.

I think that this happened in the past and somebody here knew the guy that was running the web site. I guess that 503 is a server error? Anybody know?

There are some good writeups in the Downloads area. Technical Articles maybe, or somewhere else. More than one, randomly placed in the various categories. With pictures.

Seems unlikely that 0.4 mm would be a factor but it should be easy to find out. There should be damage on the inside edge of the wheel where it was crushed against the hub weld. If you see damage, you should be able to file away 0.2 mm around the inner edge of the wheel hole to create a clearance chamfer easily. A few swipes with a round file. The pattern on the back of the wheel is also a good indicator of seating. The spot behind the lug nuts is where the force is. https://www.ebay.com/itm/186288432645?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=fN_3lKgHSjG&sssrc=2047675&ssuid=bBzFtXzvTQO&widget_ver=artemis&media=COPY

The basic problem with any reman is it's always hit or miss. The reman shops only examine the parts for obvious problems and wear and test various components electrically. There's just no way to tell how close the used part is to failure. Insulation breakdown, metal fatigue, etc. Business-wise, the only reason to introduce a new product to market is because the reman's are so bad. Take some good pictures if you have time. Interested to see what they're producing. They do alternators also. Cheaper than one of the reman's. Although, if I was going to buy a reman, I'd buy a Remy. They seem to produce good stuff. https://www.rockauto.com/en/catalog/nissan,1978,280z,2.8l+l6,1209260,electrical,alternator+/+generator,2412

There's a new option. Meaning not reman'ed. WAI Global. I don't know anything about them but the cost is less than the reman'ed BritishStarter unit. And no core required. https://www.rockauto.com/en/catalog/nissan,1978,280z,2.8l+l6,1209260,electrical,starter+motor,4152 https://www.rockauto.com/en/moreinfo.php?pk=12165009&cc=1209260&pt=4152&jsn=512 https://www.waiglobal.com/ Edit - didn't see the full post above. WAI already ID'ed. Good luck.

You might take it apart and see if it's something simple like a dirty solenoid contact or sticking mechanism. Remove the solenoid and pull it off of the slug. Here's a video. Solenoid removal starts about 5:10.

Nissan started using gear reduction starters in 1978. So that's not really a new thing. If you search "britishstarters.com" on the internet you can find reviews from people that have bought them. Here's one. Kind of what I was afraid of. They don't really describe where they source their motors on their web page. https://www.mgexp.com/forum/mgb-and-gt-forum.1/british-starters-com-my-observations-your.3110642/

There would be no "control". You might also flood the intake with vapor as the car sits in the sun. Vaporization and condensation. Engineers spent a lot of time and effort trying to figure out how to handle the vapors in a way that solves and avoids problems. I'm sure that there are people out here who've tried to outthink the engineers and ended up back at their solution after going around in circles. The charcoal canister and its control system is really simple. The hardest part of the Pathfinder mod is probably mounting the canister.

If Dave WM has found a canister from a newer vehicle that works that would probably be the simplest most direct way to go. The concept is the same and Nissan kept stuff that worked around for decades. My 95 Pathfinder had an AAR valve that was essentially the same as a 1975 280Z's (I think, it's sold now, can't double-check). Same basic shape and function.

It's a controlled leak. A small one that is only open when the eninge is off-idle. The vacuum control hose is on a "ported" vacuum souce on the throttle body.

Probably won't fit but it shows the concept. The old days when "PCV" was a tube that exited to the roadway from the valve cover. https://www.tanksinc.com/index.cfm/page/ptype=product/product_id=638/mode=prod/prd638.htm

This would create a large vacuum leak. It might even overpower the valve in the gas cap and pull a vacuum on your tank. That would be bad. If the seal in your canister cap is bad you might have a vacuum leak anyway. Might partially explain your "lean" problems. You could just block the line completely and get a two way vented gas cap. Maybe. Gas caps are hard to find. Although the seal on mine was destroyed and it was two-way anyway. Move the smell to the outside back of the car. Like the old days.