Body and engine compatability

I have been offered a free '80 300SD... of course, it is FREE because the body is a wreck and it has been sitting w/o use for several years (i.e. there are now raspbery bushes growing on it!). I have been told the engine ran well when it was last used (has 240k). I'm going to do some more checking into the engine in the next few days.

I also know a guy who has an '85 300 with a manual transmission. The engine is shot and the rear end is pretty smashed in, but otherwise the car is beautiful.

Here are my questions... what is the likelihood that I can take the rear of the '80 (which is still in good shape) and its engine and replace it on the '85? Compatible or no?