I'm going to be swapping rears in my "76 Cutlass. It's going to be the same size, 8.5 10" also, but posi instead of the open I have on it now. Anyway, I've heard that I shouldn't torque everything down until I lower the car and put weight on everything first. Then tighten to proper torque specs. Is this true? Thanks.

 

If you're talking about torquing the bolts on the suspension arms, that's correct. The reason is that the rubber bushings lock in when you torque the bolts and the arms want to be a normal ride height when you do it. The easy way is to jack up the rear axle while the car is on stands and when the springs are compressed, then torque the bolts.