healeyg

i think the GT3/2/TT motor has too much power for the boxster tranny, and the GT3 transaxle won't work with the boxster/cayman mid-engine configuration

arenared

I think the Boxster S tranny is a Getrag 6-speed derivative of the 996 tranny used with the 911 M96 engines. I believe the base Boxster 5-speed has an Audi/VW-based transmission. I've heard the main problem is that the GT2/3/TT motors don't mate the same way as the M96 engines to the trannies--different bolts/alignment/spacing/something.

Carrera GT

If you Google a bit, there's a company in Australia that has dropped a GT3 into a Boxster and re-used the Boxster transaxle. I believe a shop in the UK has done the engineering to use the GT3 trans. Cooling (and brakes) become an issue.