There's an idea... both ports were open when I unpacked the new radiator and there was a cylinder-in-block sort of foam insert. If there was another plug, that might explain a few things. These issues seem consistent with some sort of blockage.

My new lower radiator hose arrived today with a bundle of 940 stuff. I'll check it when I replace the lower hose tomorrow.

I'm still new to these white block engines.

Thanks for the all the advice so far. I just hope I can trace this before something bad happens to the engine.