if it wouldn't turn pretty easy with a crank, plugs out, I'd think something was binding somewhere, specially if the rebuilder could turn it prying on the flywheel, unless he barely turned it with a lot of muscle [I assume he gave some kind of guarantee!!] .... think over the clutch/trans install, any problems fitting things there? crank it with the plugs out and 12V jump before you try to fire it, and wouldn't hurt to put a light squirt of oil in each cylinder before hand
Bill