5/71 240Z.  Bought a pair of Corbeau GTS 2 seats from MSA, got their recommended retractable seat belt kits as well.  https://www.thezstore.com/product/5882/seat-belt-retractable-lap-shoulder-both-sides-70-73-240z  Turns out that these are from Retrobelt.com and the instructions are really superficial.  Bag of misc fasteners, brackets, etc was provided for the DIYer.  MSA said to contact Retrobelt, who declined to provide any further instructions, citing liability concerns.

The seat belt rewind mechanism mounting was my concern.  Images show it being mounted to the tool box walls or drilling a new hole in the floor.  By looking around, found a nasty rubber plug that sealed the interior from the road.  Removed it to find a clear path to the underside.  Got a L bracket from Home Depot, drilled to suit for M12 holes 70mm from each end, no cutting required. 

Used a M12-18mm to fasten the rewinder to the bracket, then a M12-60mm to fasten the bracket to the floor.  Didn't have to cut anything in the interior, floor mat covers the bracket.  Seat slides all the way aft & reclines fully w/o interference from the rewinder.

Tested this on the passenger side, now for the driver's side.  Critique my installation. 

 

You and I seem to be doing the same jobs at the same time, my seat belt kit should be here in a couple of days.

There should be a dedicated seat belt mounting hole near where you have mounted, it has the proper reinforcement to handle an impact, where you have it I think it is just sheet metal and not strong enough. Also the home-depot bracket doesn't have the strength for the job, there should have been a bracket in the kit that would work with the Datsun mounting point.

Here is the proper mounting point on the D/S on a 72/240z.

 

@grannyknot makes some great points. I used a seatbelt system similar to the one MSA sells for many years in my 240Z, but when I changed out the old seat belts in my 260Z, I went with the Wesco Performance Roadster belts (https://www.wescoperformance.com/noname.html). @jfa.series1 found them independently of my posts on them. You mount the retractor on the upper mounting point.

While I understand you have already purchased the MSA belts, sometimes you have to absorb the sunk costs and move on.

 

 

One more vote for using the factory mounting points for any seatbelt option you choose. Don't gamble your life with a questionable install. The WESCO belts are an easy install with your OE bolts and comfortable in use.

I agree that using the OEM mounting points is the only way to go. 
 

Many times over the years I have seen where ill advised shade tree mechanics have mounted seat belts and even seats to nothing more than the unreinforced sheet metal of the floorpan. In the event of a crash, the bolts will pull through, even when using large diameter washers to “spread the load”.

Automotive manufacturers engineer and design for safety. Circumventing the original design is asking for disaster.

 

Edited August 23, 20231 yr by Racer X

Here is the driver side of my 5/71 240Z.  I don't see the mount point shown above by grannyknot.  The hole that is shown, goes through a box structure and exits on the underside of the frame.  That's the hole I'll use with the HD bracket like on the passenger size.  The HD bracket is same thickness and material as the supplied bracket with the Retrobelt.  The car was originally silver.

Edited August 22, 20231 yr by kenward1000
text added

I seem to recall that not 240Zs had the wells for the seatbelt retractors. I do not know if those cars only had non-retracting seatbelts.

Of course, with that you show, it supports my suggestion above.

23 minutes ago, kenward1000 said:

Here is the driver side of my 5/71 240Z.  I don't see the mount point shown above by grannyknot.  The hole that is shown, goes through a box structure and exits on the underside of the frame.  That's the hole I'll use with the HD bracket like on the passenger size.  The HD bracket is same thickness and material as the supplied bracket with the Retrobelt.  The car was originally silver.

 

14 minutes ago, SteveJ said:

I seem to recall that not 240Zs had the wells for the seatbelt retractors. I do not know if those cars only had non-retracting seatbelts.

Of course, with that you show, it supports my suggestion above.

Seat belt retractors were introduced with the '72 model cars. It is my understanding the many/most aftermarket retractors do not fit well into the recess.

2 hours ago, kenward1000 said:

Here is the driver side of my 5/71 240Z.  I don't see the mount point shown above by grannyknot.  The hole that is shown, goes through a box structure and exits on the underside of the frame.  That's the hole I'll use with the HD bracket like on the passenger size.  The HD bracket is same thickness and material as the supplied bracket with the Retrobelt.  The car was originally silver.

Not to sound ignorant, but isn't that a seatbelt mounted to the side rail...?

4 hours ago, kenward1000 said:

Here is the driver side of my 5/71 240Z.  I don't see the mount point shown above by grannyknot.  The hole that is shown, goes through a box structure and exits on the underside of the frame.  That's the hole I'll use with the HD bracket like on the passenger size.  The HD bracket is same thickness and material as the supplied bracket with the Retrobelt.  The car was originally silver.

Your car never had retractable seatbelts, which is clear to see as the outer lap belt is anchored to the OEM attachment point. I’m not sure there will be room to mount a retractor where the belt is mounted originally, as the seat doesn’t leave much room there.

I also reiterate that attaching a restraining system in any manner other than originally designed is not a good idea. The safety of you and your passengers must not be compromised.

 

Thanks everyone for all the helpful suggestions.  The Corbeau GTS 2 and the retractable Retrobelt has been installed in the passenger side of my 5/71 240Z.  Starting in tomorrow with the same on the driver side.  California Melee is coming right up!

A final observation: the inboard mounting location for the retractor is going to result in constant rubbing of the lapbelt against the side of the seat. Good luck with your project.