If you decide to use the SM-420 with a newer engine, (which may have the newer bellhousing, the one with no crossmember under it); you could get a piece of 5" XX wall steel pipe, about 3/4" thick and have it machined down to fit the opening and press-fit on to the SM-420 bearing retainer. I have had this done, but it was several years ago, so I'm not sure about the actual dimensions.
GM Truck, four speed standard transmissions. Built by Muncie.
Installed in: 1947 - 1967 Chevrolet and GMC trucks up to 2 1/2 ton.
Model: SM-420 - Bearing Retainer/Bell housing opening size - 4 11/16"
Gear Ratios
1 - 7.06
2 - 3.58
3 - 1.71
4 - Direct
R - 6.78
Oil Capacity
5 1/2 pints
Installed in: 1968 - 1991 Chevrolet and GMC trucks up to 2 1/2 ton.
Model: SM-465 - Bearing Retainer/Bell housing opening size - 5 1/8" Gear Ratios
1 - 6.55
2 - 3.58
3 - 1.57
4 - Direct
Length - 12"
