I have noticed a difference between the 75 and 77 ecu's. Same part number but different. The 77 is missing pins and has 2 fins that stick out from the center of the connector

Correct, not sure what the question is or you just wanted to let us know but here is more information

 

Edited October 11, 20213 yr by AZDatsun

That info is cryptic. What is nmc and jecs? I assume for example if you have a 75 280 with 4 speed the ecu has to match.

Different manufacturers making the same design.  There have been a few discussions about the differences but it seems that any ECU from 75 to through 78 will work on any EFI engine.  I tried the range, except 77, on my 76 and they all worked.  The 78 ECU did crap out on me after a short drive, but I think that's why the car was being parted out.  The one thing that won't work without the proper ECU is the altitude fuel adjustment.

Here's another ECU link.

 

It’s not really cryptic NMC and JECS are two different manufacturers for the same part. Some people say you can interchange them and it’s the connector to the AFM that matters. What are you trying to solve that you think you need to swap out what was in the car?

Whats an AFM

air flow meter

 

 

 

Edited October 13, 20213 yr by AZDatsun