i like to repost PM answered questions just so people can search easier:
Okay, i read the question wrong. I didnt realize you had a GSR swapped Si. Yes you should be using a P72, but both OBD1 and OBD2 P72s will require a conversion harness. The Civic is OBD2b the ECU would be OBD2a.
If you keep the engine stock, go with the OBD2 ECU. If you plan to turbo or do some kind of serious mods (not I/H/E) then go with an OBD1 so you can tune later.