Firebob, I'm going by what I've been told and all I can tell ya is that is works. My M21 was completely rebuilt and converted to an M22 by a guy who knows them like nobody else. He was the one who told me and since then I've had a couple of other older hard core 4-speed guys tell me the exact same thing. Anway, if you do the 3rd gear before reverse trick it will not grind and or clunk and it will save a ton of wear & tear on the trans...