I didn't ask the question initially, but I'm looking to do the same swap, and have a few specific questions.

How do you mate the VW transmission to the Fiat hubs? Do you need special axles or do you use the Fiat/VW stock axles?

What about mounts for the transmission and engine? Do you start with some VW mounts and weld them to brackets to fit the Fiat engine compartment?

Is there any other custom pieces I would need?

Thanks,
Patrick
1971 Fiat 850 Spider (not yet on the road)