Drive shaft and alignment

Alright, so I rebuilt the front end of my 73, new a-arm bushings, tie rod ends, ball joints...  and I take the vette in for an alignment.  The tech calls me back and says he can't do an alignment because there is too much end-play in the drive shaft which effects the camber and caster adjustments in the rear.  I must have missed something because it doesn't make sense to me that that would be the case.  I can stretch and say the half-shafts would have a "bearing" on the adjustment, but I just can't see it from the drive shaft.  I would appreciate an explanation if anyone is willing to share. 

Might just be a terminology issue. The "driveshaft" is from the trans to the diff. The "half-shafts" go from the wheel to the diff, and those do effect the alignment. Some folks will call the half-shafts "drive" shafts. You need to have him explain which shaft(s) he's referring to. If the yoks in the diff are worn where they ride against the center pin of the diff, it can cause excessive end-play of the yokes, and create alignment problems. How much is too much is a question yet to be answered, imo. The yokes need a small amount of end-play, but not very much...maybe .010"-.012" or so. Much more than that, and the alignment will be hard to set, but not impossible....it will change as the wheels move up/down, or in corners, but not enough to really make it dangerous. If there is a LOT more play in the yokes, you need to have the yokes replaced.