It's not clear if you are going to pull and reinstall the same engine, or put another one in there.

Stating the obvious here, but you have to give a long jaundiced look at a PnP candidate if the car has no significant body damage or rust. That increases the odds that there is a mech. problem which caused the owner to throw in the towel. Might just be an electrical issue which you could resolve in the R&R process, but also could be the engine is toast.

The yard will have drained the oil, but even if the plug is gone and the pan is dry, you can stick a finger into the pan and scrape the inside around the drain plug and see if you come up with metal particles. A smear of fine, graphite-like sludge is pretty typical, no big deal. Are the spark plugs clean, not oiled up? With plugs out and in neutral, it's usually possible to turn the crank over with the fan belts, and at least make sure it turns without hangups.

The $150 or so isn't chicken feed, but more to the point, I'd be really bummed to spend that many hours grubbing around, then schlepping it home for a teardown to find I now have a 400-lb boat anchor to get rid of.
--
Bob (son's 81-244GL B21F-M46, dtr's 94-940 B230FD, my 83-244DL B23F-M46, 89-745(LT1 V8), 98-S90, 77MGB and four old motorcycles)