Th350 with 4.10 gears in the rear

[Captainfab]

If the differential in your '62 is original it is a Eaton HO32 and the gears are likely 3.90's. I would change it out for a '63-'70 12 bolt, or a '71-'82 12 bolt if you want to change to the 5x5 wheel stud pattern. There is much more aftermarket support for the truck 12 bolt and it is easier to find highway friendly gears. Either way, the trailing arm mounts will have to be moved to align with your '62 trailing arms as they are farther apart than the '63-'72 trucks. Then depending on what year 12 bolt you get, you will need either a custom length panhard bar, or weld on a mount to use your original panhard bar. Also keep in mind that the late'70-'82 12 bolts are 1.5" wider than your Eaton HO32.