Check width from backing plate to backing plate. Look at the suspension setups on both vehicles to see the differences. You would need to convert to a power disk setup with a booster and dual-resevior master cyl. Besides the welding of rear suspension brackets & stuff, you'd have to get a driveshaft made with tranny u-joints on one end and caddy u-joint on other. Also, what gear ratios are available for that rear axle? You don't want to get stuck with some weird one-off caddy ratio.
Ask questions, take measurements, check parts availability, & look at manuals for both your truck and the donor car to see what will work.

good luck

chip

Preaching the Hot Rod Gospel according to the 4-stroke apostles:

Suck, Squish, Fire and Fumes