Originally Posted by SouthArk370Z

They should be able to check the radiator before deciding whether or not to replace. Same with the pump.

If the radiator is plugged with sludge, the block probably has some sludge buildup too.

I'm still not 100% sure that corrosion/sludge is the problem (although it sounds like the top candidate). If it were me, I'd inspect the radiator and pump before I started replacing parts. I'd do whichever was easiest first. You should be able to get a good idea of radiator condition by pulling the inlet hose and using your borescope.