[Captainfab]

The original '60-'62 small block with an manual trans motor mount, is a front mount at one point only. The '60-'62 small block with an auto trans were side mounts, but are completely different than the '63-'72 mounts. They obviously have to be configured so as to allow for the center of the motor mount being on the rear edge of the crossmember. A 283 is no different than the 350 you have as they are both small blocks.

If you want more of a bolt in motor mount, you will need to use the '63-'72 truck motor mounts, and the '67-'72 small block motor mount brackets. Those brackets will fit the shorter frame height of the '60-'62 trucks and be in the rearward location. Here is a pic of those brackets on a '62 GMC frame.