Google sm420 and look at the pictures. Keep in mind depending on the year of the truck the rear bearing and yoke will be different for the torque tube type driveshaft then say an open drive line. Some heavy trucks might have a ebrake assembly off the rear yoke as well.
You can always post a picture of your top cover too.

Last edited by sstock; 07/10/2018 8:28 AM.
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