4 speed noises .. help!

Ask your mechanic this, when he went to a shorter drive shaft (which you have to when going to an 8 3/4) where did he position the tranny slip yoke on the splines before taking the tranny yoke to pinion yoke centerline measurement. If you see his eyes get all wonky like he's thinking to hard or he just can't come up with the answer don't drive the car and find yourself another drive line mechanic.

Terry