Alignment Problems

[68Custom]

Well, heres the story..... i had my truck put in the shop for a complete rebuild on the front end, including new steering parts and chassis. Things went together right but when it came time to have the alignment done it went down hill. The toe and camber went very smoothly, but when the caster was being done, they had nothing but troubles with it. Is it possible that the two upper control arms are not identical from each other causing my caster to be off by say 10 degrees? What i mean is, is it possible that if they aren't identical could someone have switched them around causing the problem in the long run? Or is this a sign of possible front end collision coming to haunt me. I have seen no signs of my truck being hit anywhere. The shims for the control arms were ground down so now the caster is sitting at 8 degrees on one side and 9 on the other. Needing some info on what to do, appreciate all replies! Thanks!

Aaron