Nick Yoskin can help you out with a nice top mount kit if that interests you. Having turbos up front should help larger turbos spool nicely and make as much power as your heart desires and tires can hold.
With rear mounts, I am guessing the A/R has to be lowered, but is partially compensated for by having no real exhaust behind the turbos. Having a lower A/R and roller bearing journals will help with spooling. I think East Texas Muscle cars is doing twin GT35r's.