I set my frame level on jack stands and set the engine/trans at 6 degrees. Then I installed the rear at 6 degrees. I didn't have any body parts or any other heavy stuff to preload the suspension to adjust for rake, but I figured in 2 degrees for rake to hopefully end up with the desired 4 degrees of pinion angle when the truck was fully assembled. It's not all that important to go more or less than 4 degrees, just that the trans and the rear end are at the same angle,
Scott