New 8 1/4 rear

There's not a fool proof way to tell if it's good or not but just spin it over by hand and feel if it spins smoothly. If it has rough spots that could be a problem. Also wiggle the axles up and down to see if there's any play in the bearings.

A couple of things can happen when a rearend goes out. They can either make alot of noise or they can stop going all together. I've even seen them gernade and blow parts out the back.

Yes all A-bodies are set up the same but like Mr.318 said the shock mounts and U-bolts are different size for different rearends.