The days of stuffing a used unknow motor into a car and driving it are over. This stuff has simply been sitting too long to expect that to be a good outcome.

Rings, bearings, gaskets, a quick hone and clean up was a $200 "rebuild" back in the mid 80s, adding a cam & lifter kit was another $150. Timing chain and gears added another $60. That was back when a real rebuild was $2,000 + depending on how carried away you got. I did a ton of abuse and 60K + miles on a lot of those $450 "rebuilds".

So that cost has jumped to a grand now, when a full on rebuild is 6 grand +. OK! Still looks like a deal, if the basic motor is sound. Find out if the motor is sound first, check the bearings. A leak down test on a motor I'd be re-ringing wouldn't give much useful information, except maybe the possible condition of the heads.

The motor was in a mud truck, Over heating or under water would not be an unexpected event, it did have a hole in the oil pan, water probably got in there. A quick hone & rings, and rod & mains would be expected, as long as the crank and rods are still good. The heads and a new cam are over and above.