I'm currently rebuilding a sbc 350 with casting number 10054727. I'm trying reinstall the pistons with new rings and they are very hard to move once the compression rings are in the cylinder. The only way I can slide them further into the cylinder is by hitting it with mallet. The piston ring gaps are correct (checked with a feeler gauge) and the pistons are original to the engine. Every video I have seen of pistons being installed, the pistons can almost be pushed in by hand. Any ideas as to what I'm doing wrong?