Oil pressure problems.?

You have two separate problems, the fist one you need to address is the over heating. Rent a pressure tester at auto zone and doi a pressure test for leaks. If it don't hold pressure and you can't see a leak remove the tester with the cap off start the engine and look for bubbles in the coolent. Bubbles= leaking head gasket or cracked head. If the system holds pressure have a radiator shop clean the radiator. Odds are after you cool it off oil pressure will be OK, if its not replace the pump with a Melling high volume pump. Its easy to change. Its what the filter screws onto you'll know which bolts to take out by the new pump. Change the oil with a new filter before starting the engine.

It is extremely unlikely that your engine overheating problems are related to anything having to do with oil pressure. You should be focusing on your cooling system. You changed the water pump and thermostat so you are pretty sure those are not causing any problems. That leaves the radiator. Radiators get plugged up and lose their ability to cool. Have someone check the radiator with a flow test. You may have to have it steam cleaned or recored if it is too plugged up. A new radiator may be cheaper in the long run, if still available.

It is normal for oil pressure to drop when idling with a warm engine. Oil is thicker when cold and thinner when hot, this affects oil pressure. Remember that the engine drives the oil pump and the faster the oil pump turns the more pressure you develop. This explains why your oil pressure is lower at idle. Do not worry unless the oil pressure drops below 15PSI. My Dodge 318 oil pressure varied from 20PSI to 45PSI , depending on temp and engine speed.

You can try changing the oil pump, because on that engine it's on the outside of block. But you could have a plugged pickup screen, or the engine could simply be tired.

Depends on what your real pressure is the guages on the Cordoba are not reliable. and oil pressure drop will not cause an engine to over heat, maybe seize do to lack of oil pressure but not enough to over heat, it would seize first

I believe you should have around 40 pounds of oil pressure at idle; if yours has a guage instead of an idiot light, you can check it.