Depends also on what your running out back , leafs springs, or 4 link ,ladder bars
http://www.quickperformance.com/Pini...ent_ep_45.html
http://www.hotrod.com/how-to/paint-body/91758/
leaf springs 5-7* static angle , under power the rear will rotate up
no limits video shows the same and also CPP tech page 271 in their catalog
At work I've set the drive shaft angle of diesel and electric AC- fire pumps for oil rigs high rises ect. for 10years.The instruction are very clear to have 3* of angle on the drive shafts for the u joints to function properly. They are rigidly bolted down with no movement to very stout I-beam frames.