Heres a little info that may help you, as I was contemplating sticking one of my spare 6.2's into my '68 C-10. The mounting points on the 6.2 correspond to the points on a BBC. In the later trucks that they came in from the factory, they used the BBC mounts (the "clamshell" that mounts to the side of the motor, and the rubber/steele shell that is mounted to the perch mount on the frame). It would be an easy enough setup to do on a '63-up truck. I havent considered what it would take to do on a torsion bar '61 frame, but it couldnt be too difficult.
I'd start with the perches from a '73-'87 truck, get them in the right place on the frame, the rest should be fairly straitforward. Let us know how this works out.
