Nile, thank you for starting this thread.
I have an interest in switching the stock TC rims for the later generation, five lug Biturbo rims (photo below). I have seen these rims listed at 7x15 (7Hx15H2) ET 35 or at 15x8 1/2", although I think there is even more variety from ~89 - early-90s (they look like they were 14" pre-1988, which is too small, I think). My fear is that the Maserati five lug pattern isn't compatible with the TC. I haven't found the definitive answer, but I have read in some VW forums that the 1980s Biturbo wheels may not conform to alot of other makes.