I don't know which one you have but I can give you some info so you can figure it out. I'm assuming you have a Gen II 3SGTE.
1-US Gen II 3SGTEs have a heater wire for the O2 sensor, JDM ones don't. So if you have a 1 wire O2 senor you have a JDM ECU. If you have a 4 wire, you probably have a US ECU, though it is possible to have a US harness with the heater wire connected to a JDM ECU.
2-92/93 ECUs have a second circuit board above the first. It's for more detailed diagnostics. So if you only have 1 circuit board you have a 90/91 ECU. I believe that goes to 91/92 and 92 - 95 for the MR2?
3-The RC ECU has a pin for the intercooler level sensor. It's an open spot on all non RC ECUs. I don't remember which connector off the top of my head, but look it up, and if you have it, you have an RC ECU [or very slightly possibly a CS or Grp A]. If not, you have a regular ECU.
4-JDM engines came with a EGT sensor after the catalytic converter. If you have one, you have a JDM engine.
The US and JDM ECUs are plug and play with each other as long as you have the same revision [90/91 or 92/93] with the exception that a US ECU will throw a O2 heater code with a JDM harness.
The RC ECU is plug and play with the 92/93 ECUs except for the intercooler level sensor.
IIRC the MR2 ECUs are also plug and play with the same revision Celica ECU, but I'm not positive on that. If not very close.
The 2 revisions are very similar wiring wise. only 5? wires are different between the connectors, and either will run either engine just fine.
That's all I can think of right now, hopefully that helps.