There are differences from year to year and car model to car model. Most of the parts from any D-jet car will fit any other--but that doesn't mean they're right.
Examples: The 1.7 injectors (yellow, I think) flow less fuel for a given electrical pulse than the 2.0 injectors (green). The 71 Type III MPS will cause a 74 2.0 to run VERY rich. And so forth.
If you have a 73 2.0, you may want to use 73 2.0 parts specifically. If you can't find those, the 74 2.0 parts should work fine. If not those, the 75-76 2.0 parts will work fine. You can mix-and-match them to a certain extent, but you will probably be making subtle changes to the way the car runs. They may be too subtle to notice, though.
If you look through the Forum on the 914 Club's page
http://www.dgi.net/914 , you will find a list of MPSes and ECUs by Bosch part number. I think I put it in "maintenance" or "question". (Click on one of those words in the banner.) That will at least show you what other cars had equivalent parts.
In general, I would suggest getting a complete FI system off of one model-year's car. If you can't do that or it's too expensive, you can try substituting. But I would think that the ECU and the MPS would need to go together.
Good luck!
--DD