re: >>I think he meant 996 engine upgrade.<<
Actually for the 2.5L I was thinking a non e-gas engine to keep the motronics compatible. Someone with your experience may be able to do this right. A lot of shops that think they can put an e-gas engine into a non e-gas car may find themselves in over thier heads mid-install. Also the older engine may be cheaper.
No expert here - I sure wouldn't want to deprive a Boxster owner of MORE POWER