I encountered similar problems when working out my options on my Valkyrie. the corvair suspension just is not adequate for the fitment of any other gearbox than the Corvair. Once you step into the Audi or Prosche realm, you should look at using Fiberfab's UMETS system or a similar style linkage suspension or adapted street car suspension. If you were moving to a Porsche 6 spd. or similar I would take a look at using a 993 Porsche suspension. It has some beautiful aluminum pieces and it is easily adjusted. It could also be used to create an entire removeable sub-frame with some fabrication, much like Fiberfab's UMETS system.
I did some brief measuring and it would fit with some modifications in the back half of the ole Valkyrie frame, depending on which model you have. The good thing about that car is it is not too space constrained. Lot of options, might as well be creative.