I suppose you've seen this
Pelican article which has info on the 2003-2004 cars? Before I decided to have my shop rebuild my 2003 S engine, they had a totaled 987 Cayman S with a crate 997 3.8 engine that was being parted out. They said it would work in my car with the ECU, but I passed as the total cost was way more than I wanted to spend. But they said it would work, which is consistent with the article. Good luck, I feel your pain!