Swapped 8 3/4" pigs, now axles won't seat fully?

It could also be the splines in the diff that is misaligned. This would happen if you turn one axle without having the other axle installed. Hook up the driveshaft, put the shifter in Park, install the axle as far as it will go and use a long prybar to turn the axle while pushing inward. The clutches in the Sure-Grip should slip enough to allow the splines to line up.