Small Block & Big Block Chevy Specific - 305 SBC being rebuilt, rotating assy won't move after #8 piston

a friend of mine is rebuilding a 305 chevy i have out of a 1983 pontiac trans am. it spun a rod bearing but i had the rod cleaned up and we had the block looked at and it looked ok. put in all new rod bearings, new rings, etc. and everything was ok until he put in that #8 piston. for some reason now he can't manually turn the rotating assembly. any idea what would cause this?

so as it turns out, the machine shop put the rod back on the piston backwards :bang: and that's why it wouldn't move once installed. he took the piston out and put it in backwards so the rod is now correctly installed and now the rotating assy turns just fine.