Looking at combining two cars. An '80 Fi with a trashed body but with good mechanicals and a 78 with a good body, but not so good mechanicals. Is it possible to drop the '80 engine and tranny into the 78 body?

Yes and with plenty of effort the fuel injection system can also be grafted into the older car. Prepare for some healthy work ahead.

Hey Bruce, you looking at a winter project for the new garage?
Yes it is quite do-able,most/all parts are interchangable. Now you can have a "franken-fiat" as well. As mentioned you can even splice in the FI system, or take the 2L block and 1800 head,single plane manifold and a 32/36 carb or 34 adf(I'll call you about that), 2L exhaust manifold and down pipe if the 1800 is 4-1 type.
Have fun
Should have gone to the docks for your fish this year .. $10.00 each for whole sockeye salmon (have 10 in the freezer so far)
Chris