I did this swap 2 years ago. My conversion went flawlessly.

I hired a welder to do the modifications to the perches. He set up a table jig to mount the old rear end, and then used my new perches that I bought, to align on the table to weld in to the new 8.5 rear. Mine was out of a 1973 Nova. The new rearend fit perfectly when I installed it.

I installed a new driveshaft rather than try to cut and rebalance an old one. My new driveshaft with new yolk cost me $185 bucks, balanced. It was better than my alternative. The old driveshaft was out of balance, and he could easily had that much cost into trying to balance and straighten the old one.

I used a string to measure the distance when the car is planted on the ground from end to end. The driveshaft guy told me how to do this. Then he made one to exact size and it fit perfectly.

I bought all new leafs, and shocks while I was down there.