I have read on this site about the water pump impeller being loose on the shaft.. Might want to take your water pump off and check it..

Ditch the flex fan as said above more than once and use a good stock fan with a good clutch fan...

Good guesses. They involve both time and money that may not be needed if he gets a temp gun and finds out what the temperatures look like.

If the impeller was loose then water would not flow. To check that all he has to do is remove the cap and see if coolant is flowing.

Let's say the cooling system is ok.

What could be happening inside the engine that makes it such a high BTU water heater???
I'm just curious, I have seen in the past some engines just make a lot more heat than others and I've always thought that it has more to do with tuneing and the Cam setup ( when the obvious issues are addressed and taken care of like intake leaks and stuck stats, poor or missing shrouds etc. ) these things can answer a lot of questions and save the OP time and money.

Timing and lean condition, the alcohol racers have a valve they open to let more air in (lean) while running to make it heat up faster. Detonation could be a problem, try different advance settings. These engines where made for 260 Sonoco not the junk we have today. Basically burns at different speeds. Did anyone install a non stock cam? If so it could be installed retarded. There are so many places to look so try the IF gun first.