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

Might be the split/side gears inside the sure grip are not aligned.

Put both axles in, have someone lever/crowbar one side to hold axle from turning and give the other side a quick jolt either direction. See if the axle seats in further.

Bingo! This was my thought. Do you have stock tapered bearings or Green style axle bearings?