Good info to pass on Jerry, I might add that if he plans to retain the parking drum and related appurtenances, of his bigbolt he will need the top loader off the original transmission unless the donor trans has the shaft for the brake handle. I have never seen a fine spline sm420 but a couple late models have them.Also even the sm420s found in 1/2 ton had a side cover pto provision that is identical. Basically sm420 from 1/2 tons on up to 2 tons are identical sans the rear bearing cover and ujoint for the enclosed driveshaft, and top cover for the hand brake.

Like Jerry says save the yoke and bell type rear bearing cover found in 1/2 and 3/4 ton trucks pre 55, getting hard to find.

Last edited by sstock; 01/17/2020 5:36 PM.
1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration