Bob:
About a year ago I installed a Legends 5-speed in a 66 Biscayne. Aside from the torque capacity consideration which wasn't super important to me, as I am not using the car hard, I was impressed with the fact no trans tunnel modification was needed. The Tremec I measured up for the switch just would not fit without modification to the trans tunnel. I did have to shorten the drive shaft, relocate the trans crossmember and use a special front driveshaft spline yoke with the Legends. Legends offers a number of trans with a variety of shifter stick locations. One negative, pretty expensive. BUT works great with the 3:73 rear gears and you can cruise comfortably in the 70 plus mph range