Use an OBD1 P72 ecu, it will run the OBD2 motor just fine. The differences are actually very minor, with OBD2 simply having more sensors but when you are using the OBD1 ecu it doesn't look for those sensors so no need to worry about them. You do not need a conversion harness with an OBD1 ecu. So don't use an OBD2 ecu, that's what I'm getting at.
Mainly the differences are:
1. crank fluctuation sensor
2. secondary O2 sensor
Neither of these are used with OBD1 and can be ignored. The other main difference is the plug style of the injectors. You can swap plugs to OBD2 style, or just swap to OBD1 injectors and keep stock plugs.

It is no big deal putting OBD2 into an older car unless you try to also run the OBD2 computer. Use a computer of the same vintage as your car and there are few hassles. Also the engine will fit fine, externally all the mounts are the same.