so what do you intend to use for a transaxle in the rear? A Mendeola-style or a Porsche box? The G50/50 or G50/52 tend to be really long and the hi-strength Mendeola is pretty long too (I know as I have a full tube chassis Porsche 914 with 525HP SBC and Porsche 930 box - was looking for options other than the dump-truck-like-shifting of the 930)...
I had a 1970 Grabber Sportsroof that I sold to go to college 7yrs ago and my next project will be a crazy 70 fastback - not mid-engined but I have some crazy ideas of my own so I appreciate what you have going here! Should be a cool car. I will just say a "torque tube" will be involved in mine