I've used the C5 drivetrain in several builds. Ive had a machinist friend shorten the torque tube. For one of them. I shortened it by 23 inches. It was not a problem. I I put a lot of trouble free mikes on that set up.
I built a Cobra replica using C5 parts. I had my friend machine an adapter that bolts to the front of the diff and accepts a driveshaft. I used an LS6 engine, a tremec 6 speed, and the C5 diff with the driveshaft. The set up works great.
I had 2 extra adapters made at the time. If you need one I would be willing to sell one.