If your friend does not want to change the rear end he will have to use the original trans. He will have to use an early chevy cast iron bell housing. They have mounts at the bell housing. The 55 thru 59 truck would be best as I believe the mount to the crossmember is the same as the Advance Design trucks. Also the truck bell housing bolts through the bell housing for the bottom two transmission bolts. If he uses the stock bell housing, he can use the stock early front mounts for a 59-59 truck, and fab a simple front crossmember.
In 1969 I had a 49 GMC with a corvette 283 in it. I ran it hard and street raced it a lot. The rear end held up with no problems, although I did break the U-joint once. Not really the U-joint, but the splined portion of the joke. My truck was a 4-sp model. I do not think the stock 3-sp will hold up to anything more than normal street driving.
Hope this helps.
