I wouldn't switch "makes" of engines although I suppose with enough fabrication work you could probably convince the powertrain from most small FWD cars to fit - but fitting is only the start - getting everything to work would be a bitch!
How about putting a 472 or 501 out of an mid 70's Eldorado where the back seat currently is and drive the back wheels (you'd need to use the Eldo tranny to accomplish this and figure out a front suspension) - hey - it'd be unique!
I'd stick with an 8V or 16V CIS injected engine - why make things tougher than they need to be. A 16V bunny can be a sweet ride. As to where to get an engine - there are places on the web that deal in used engines - if your '79 is a 4speed this would be an ideal opportunity to convert it to a 5speed box as well.
Diesels - IF you had an entire donor vehicle it wouldn't be a bad conversion - you're changing out the power train, the entire fuel system (tank to injectors), removing the igntion system, you'd need to do something about the glow plugs, the gas tach wouldn't work with the diesel signal so you'd need a diesel instrument cluster (helpful for the glowplug indicator light as well) and you'd need the diesel engine / tranny mounts (more stout than the gas ones, to deal with the vibration) - you'd also end up with a car that's slower than what you started with - the turbo diesels (MK2) were, however, very nice and accelerated pretty well.
There's my two cents -
Steve