Welcome, Okie! Nice to have a couple of donor engines, eh?
When you got your '79, did it have the carbs and/or the exhausts removed? I bought a '77D a few years back that had been sitting outside for years with no carbs and no exhaust. The motor wouldn't turn over because some of the valves had been open and water had gotten down into the bores, and over time cause enough corrosion to seize things up. When I dismantled the motor, however, I found that I was able to free up the pistons and they came free from the bores without scratching things up much more than they already were. They were serviceable, but my goal was to install a Wiseco 750cc kit, so I had the cylinder block sleeved. The rest of the engine was in excellent shape.
So, just letting you know that there's a chance, at least, that you 79's motor may still be serviceable. You can try pouring some Marvel Mystery Oil down through the spark plug holes and let it sit for a week or two, then see if it'll turn over. Can't hurt, I reckon.