Your car being lower than anything that came after is no surprise, even the small cars these days need a double decker bus license to drive (or a periscope to see above the dash).

Your cooling problems are unfortunate, but not to be unexpected at it's age. Can be hard to discover exactly why sometimes. We'll start with checking for a leaking/blown head gasket. Check the oil on your dipstick and under the oil filler cap for a milky white or brown frothy/sludgy consistency after running. Take all the plugs out and check for water droplets on the plugs and while they're out, crank the engine over to see if you can detect any water mist blowing out, wipe around the spark plug tubes with your finger to check for moisture. With the engine cool (NEVER remove the filler cap when hot), remove the cap and start the engine, fill to just below the filler neck and watch for bubbles in the water or water being blown out the filler in gushes as the thermostat opens. Get a compression test, or/and a cooling system leak down test.

Most usual place for blockages otherwise is the radiator, old hoses and that metal tube across the back of the engine. It's all a matter of a process of elimination. As an educated guess, I suspect your radiators stuffed.