I know it's possible to put a 2000SVT ECU into a late 99 with returnless fuel system.

Granted the dealership didn't think it would work but they did it anyway for me and it did.

Besides that I am of no help so i'll stop typing now.

04 Subaru WRX "Eurosport bling bling fast and furious tokyo drift" "They have diarrhea of the mouth, and constipation of thought"