Grant, I just gave one away a few months back and it shared the same bellhousing as the sm420. It came out of a 1953 GMC 450 series. I believe it was a 207VO model. It didn't use the SAE pattern. Maybe later models did, but not these ones.

Jeff

My 1953 Chevrolet
1947.1 Gallery
1972 C-10 1/2 Ton & 1972 C-30 1 Ton