You're dealing with a blacksmith, not a mechanic. Take the rear end somewhere else.
The goal is to create a straight line from the back of the crankshaft through the transmission, driveshaft, and the pinion of the differential under load!! Due to the tendency of the pinion to rise under load as the pinion climbs the ring gear, there MUSt be some angle present at rest.
How well the rear suspension controls the position of the rearend is the most critical issue that determines how much pinion angle will be needed. Some types of rear suspensions offer more control than others and require different angles. A ladder-bar suspension normally requires ½ degree of pinion angle, a four-link requires 1-2½ degrees, and a leaf-spring suspension requires up to 6 to 7 degrees. That's negative pinion angle, i.e., the pinion is nose-down in relation to the driveshaft.
It was fine when you got it back from him the first time.
