WORTH MY TIME TO LOOK

actually, you can. All the body mounts line up except for the front bed mount, which is off by 2 inches. We put a 99 2500 ram frame with cummins under a 77 w200 body and bed.

believe it or not, the Chevy suburban body mounts also are very close, with the rear cab mount and the middle bed mount being off. Everything else clears just fine.
What's the difference in the frame from a '70 to a '77 though? I would think they have quite a bit of difference.