Two much stuff in front of a radiator that might be too small is my first thought.

I know that when I put a trans cooler in front of my 67 mustang radiator the temps went up and when I took the the ac condenser out of my truck it ran cooler than before. Maybe moving the coolers off to the side or making sure they are spaced off the radiator at least. The fins on those are usually pretty tight together making it harder for the fan to pull air through the radiator especially if the fan is far away from the radiator.

All the smallblock upper pulleys that I have ever paid attention to have been the same size. Maybe they change speeds with the bottom pulley instead?

If you do go with another pump try the edelbrock or at least another one with the disk on the back. I have an edelbrock pump and milodon thermostat on my daily driver and like it a lot. It warms up fast and stays there. I have just the factory dummy guage, but I have stuck a cooking thermometer on the cylinder head and radiator on 90+ degree days and it gets to about 195 or 200 at most sitting still.