the thing that throws me is the tach internal swap. The 240z and 280z operate differently . One is current driven and the other voltage . Trying to follow wiring practices for an early tach wiring might now work for your set up. My early tach worked fine with no additional wires for the tach. I wish I could be more help , but the zx dizzy swap I did was a hot for the coil and then connecting the connector wires from the dizzy- done. 

Yeah, the thing that broke was the only magnetic thing I took out of it... I don't claim to be an expert here though. 

Also the internal swap decision came from reading a bunch of posts how the stock tach doesn't like the electronic distributor. So it's pretty much just a 280ZX tach with a 240Z housing and face plate, that works with the 280ZX distributor.

The tach arrived at my local post office today, so hopefully it will come tomorrow!

Then moment of truth.

So you have a stock tach in there now and you haven't seen it run so you don't know if it works. Just saying that my current type tach worked fine with the zx dizzy. I wouldn't swap tachs until you get it running or you might really be chasing your tail

My stock 240 tach works great with the ZX distributor. The fonts are so different, I'd think the ZX one will stick out like a sore thumb. My $.02 worth.

Well the distributor came in and the car fired right up! Just need to run the signal wire then we will see if the tach works.

Also I used the 240z faceplate so it looks completely stock.

So I just ran a dummy wire to test to see if the tach works.

It's PERFECT!

No jumping, very consistent and steady. Moves well with rpms. No issues what so ever. It's smoother than my miata's tach.

Thank you all for your help!

-Josh