Grant,a properly installed NOS type rope seal will have enough drag so the engine assembled with crank only will need a bar to rotate it.But the starter motor won't have a problem turning it over.
Did you install new mains,drop in the crank,torque it down,then try to rotate the crank? If all is well,the crank will rotate easily by grabbing the front snout with one hand.Then take out the crank and install the rope seal.
