My '62 C10 came stock with the 235 and a 3 on the tree. Some previous owner ditched the 235 and installed a 250. They also dumped the 3 Speed and added the SM420 4 speed.
When the 250 died, I dropped in the 1967 327 I had in the garage. I used a couple of '63 and up side mounts to put the 327 in. I used the existing holes in the frame and had to put in a 1/2" shim to take up the difference in height difference between the X-Frame and the Ladder frame. There are correct side mounts out there, but they are hard to come by. I also had to drill 1 hole per side in the front suspension crossmember.
A Small block Chevy swap works well in the '62 X-Frame. If you have any questions, feel free to ask.
