You might want to rethink using the T56. It is a double over-drive trans with a forth gear of 1.0:1, fifth gear 0.74:1 and sixth gear of 0.5:1 and with the Dana 44 with 3.07:1 a final drive ratio of 1.5:1. Even with a #2000 car, that 250 is going to have trouble pulling that. The Camaro probably had 3.50 gears.
The T56 has electric speedo and electric reverse lock-out. Even if you had all the correct parts for the Dual-Mass flywheel, it only bolts to a crank with one-piece rear seal.
A T5 is a cheaper and easier choice, but still has a .70 over-drive.
A Richmond Six-spd would give you the extra gear, but again a .76 over-drive.
I think with any of those you would end up with a rear gear change.
Richmond also has a couple of 5-spd boxes and one, called a 4+1, has an under-drive fifth gear of 1.1:1
You shouldn't have to change rear gears.
Uses speedo cable.
Uses standard bellhousing and clutch.
