Crew cab onto a RCLB frame

[patdaly]

My eyes are bleeding from searching, I found everything but what I wanted, so here goes.

I am finally about to embark on my dream, a CCSB 4X4 square body. What I currently have is my poor old rusted out 79 GMC K20 with the Cummins 4BT. I also have a nice 83 SB, and what brought it all together, a completely rust free, painted 77 Chevy C30 crew. The only real issue is the C30 has been slammed into the weeds, so what I want to do is pull the body from the K20, mount the CC 77 cab, and them measure and cut both the 79 frame and the 83 SB frame to put it all together.

I won't have the 77CC C30 for about a month, so I can't tell what issue I will run into trying to mount it. I would assume the front body mounts are in the same location, but what about the rears? Will I need to cut them loose and move them rearward?

Any help will be appreciated, i almost wish I could find a K30 CCLB frame to start with, but those are ultra rare around here.