[elgyqc]

That looks like the rear end of an old F1 car welded to the front half of a boxster... cool.
I can't answer all of your questions, but I can say the 6 speed bolts to an engine just like a 5 speed (I temporarily had a 2.7 engine in my Boxster S and there was no problem attaching the transmission). In your case I assume there is an adaptor plate in there. On the other hand the half shafts are further back then on the 5 speed, that's why Boxster Ss have a longer half-shaft that runs at a greater angle. The flywheel position is the same, but you need at least a clutch plate for the 6 speed because the splines on the transmission input shaft are different. If I remember correctly I ran the complete clutch (flywheel, clutch disk and pressure plate) from the S when I had the 2.7 installed, it bolted to the engine with out any problem.