I did this conversion a few years ago with an LS3 motor. I documented most of the build on my You Tube channel and on 986forums.com:
https://www.youtube.com/channel/UCKSGnHyrCXAgDtJnI9siQww?view_as=subscriber
BoxsterLS376 introduction - LS3 conversion  - 986 Forum - for Porsche Boxster & Cayman Owners
Should be quite a bit of good info in there, feel free to PM me if you have any questions.
Good luck
J
__________________
John~
2003 996 Turbo... 128K Daily-ish
2000 Accord V6... 275K - 65K motor/trans now given new life!
|