The 2 block drains are in the middle of the block near the oil pan and have been hex headed on any original block I have seen. The oil gallery threaded plugs are recessed square so a small socket wrench extension will fit them. There is a unique male headed square plug on the front top of the block near the timing cover you see on Flint built engines. If you see a recessed allen head socket plug I would suspect it was put there by someone well after the engine left the factory.