I looked into using a Porsche C4 transmission a while back. This is a relative of the G50 transmission and is therefore very big and very heavy but more than capable of taking 600bhp plus everyday.
The 964 C4 (G50/50) system uses a solid torque tube to connect the gearbox to the front diff. This is a problem in a bug as the 911 wheelbase is shorter than that of the Bug. You would have to make an extension.
The 993 is similar and it was only in the 996 C4 that Porsche decided to use a prop shaft instead of a torque tube. You can imagine how expensive the 996 stuff is as it's only been on the market for 4 years.
The guys at Autocavan used a Porsche transmission a while back before the C4 was around and modified it to add a drive comming out at the front (nosecone) of the gearbox. I can't remember what fornt diff they used but it was on a very heavily modified 1303 bug. This was built as a rallycross car. Some of you may remember the progress reports which were featured in Volksworld.
Ah the days
MG