Spring compressors would definitely help with this. With compressors you can bolt the ball joint to the wishbone, compress the spring, line up the hub to the ball joint, and then lower it on to the joint. Putting the ball joint in first and then bolting to the wishbone is almost impossible as the suspension drops so low. It causes the ball joint to sit at an angle so the bolts won't go through the hole as they aren't perpendicular to the holes in the plate. In the end we used a trolley jack to raise the ball joint up to the wishbone, and greased the hell out of the bolts until they slipped over. Total PITA.
Unless I'm missing something about how to get these together?