I've seen those fat-fendered Swedes with hot small-blocks in 'em, and stock frames and suspension, with no problems. Your Caddy is lighter than a big block Chevy, I would think it would work in there without a frame swap. Unless, of course, yours is just toast. The body doesn't look that bad, the chassis should be rebuildable.
S10 frames have a huge "kick" behind the cab, car floors are flat back there. You can put in a new floor, but the back seat footroom disappears.
Gotta love the "Fat-Fender Ford" look of that body!