The hard starting might be a few bad glow plugs (check resistance to gnd at connector) and you might need to leave them heating longer, up to ~30 sec when the relay clicks off. The glow lamp going out is just an advisory for when a new engine might start.

Diesel doesn't seem to go old like gasoline. I got a used engine off craigslist that had sat who knows how long and it started right up after priming. I then ran it off the fuel in my 1985 300D that had been sitting for 3 years awaiting another engine. As long as no water in the fuel to grow biological slime, diesel should be good for a decade. I wonder why the show the Living Dead (filmed around you) doesn't leverage that. They show gas engines starting up after sitting for 3 years, which is a stretch. An old M-B diesel with std tranny or old automatic that can be roll started could still start and any fuel you recover from semis would still be good.

The sound is hard to pin down. It could be something simple like a flexplate bolt hitting the block or a front engine component hitting a bracket (like alternator fan). If all they did is boil over the coolant, but didn't run out of oil, I doubt that would hurt a cast-iron block & head engine. The overhead cam would be the first to go from lack of oil, and probably from extended overheating, and that would be a fairly easy, cheap fix. As far as parts being cheap, your engine must be better than my 617.952 turbo. These aren't Chevy small blocks.