screeching engine?

My revised first thought is that the water pump gave out. Usually leaks, but the impeller may be grinding on the block or water pump casting causing the screech. Grab the fan and shove it into the engine and turn, then pull out and turn. If you can feel any grinding it needs to be replaced.

Drain out the antifreeze, replace with plain water. Let set for a while. Check for external leaks. No external leaks, wait 24 hours and check the water level again. If the water level drops you have a crack somewhere in the head or block.

If the water pump is bad I would check for resistance via my first suggestion, turn the engine over by hand with the spark plugs out. No unusual resistance, replace the water pump and give the engine another try.

No unusual resistance when turning the engine over by hand. Leave the spark plugs out and use the starter to crank the engine or 20 or 30 seconds. Check the oil pressure gauge while cranking. You want to see the oil pressure gauge needle move up - good sign - the engine didn't loose oil pressure.

I'm surprised someone else hasn't jumped in with suggestions on this problem.

What was the oil pressure just before you shut off the engine the first time?

How hot the engine has to be before it's ruined? If the coolent wasn't boiling that's probably not the problem. However, you can have an overheated cylinder and still not get the total coolent temperature above boiling.

First thing I'd do is remove the spark plugs, squirt some oil on the top of each piston then see how difficult it is turn the motor over with the hand crank. No hand crank - jack up one rear wheel, tractor in high gear, turn the rear wheel by hand. This should tell you if you have a seized/seizing piston.

I would pull the head and pan. Remove the rod caps and pull each piston - check for scoring. I'd also main bearing caps. Then pull and check the oil pump.

Where to go from here depends on you mechanical ability and experience.