If its from 1979, its likely an 8274. The '74' in 8274 indicated the year they started making them.
Is it worth it? You betcha. The 8274 is the best 8000 pound class winch out there, hands down. You would be hard pressed to find anyone (anyone who has actually owned/used one)who would disagree with its performance. The weight differences between an 8274 or a M8000 is negligible at best (without cable), and you can use synthetic line on both. Not to mention its free.
The only downside is the physical size (much taller) and forward mounting of the winch. It usually requires a little fab work, or a 8274 specific bumper to get it mounted up solid.
I got mine for free also, which allowed me to put a little money into on the rebuild (gasket kit, etc). A little elbow grease, a few parts, a rewire on the solenoid pack, some paint, and its as good as new.