1990 USDM ST185 to SW20 Power FC conversion questions

[OutToWinPAHC]

I am doing my research on tuning options for my 1990 all-trac and I rather not piggy back it. My background is Nissan RB and GM LS series engines., so this is a very new animal to me I have found this here http://www.biststone.com/coyote-mr2/...en2togen3.html and I would like to use a Power FC. The issue is that this write up list 91-92 to 94-99 gen3 ECU, but I believe they are talking about 91-92 MR2 to gen 3, but I am not certain. I then found the extension harnesses which also say 90-99 MR2, 91-93 ST185, 94-99 ST205, is the 90 ST185 ECU and harness very different? For ease of converting back I think I would buy the extension harness and perform the pin changes there instead of the engine harness.

Does this wiring work for converting a 1990 USDM model to Gen3 for use with the Power FC or would I need to get a gen2 or gen3 MR2 harness first? Basically how do I take a 1990 USDM all-trac and convert for use with the SW20 power FC? All info is appreciated from this newb