I do have a 5 blade flexalite fan connected to the water pump & with the OEM fan shroud on as well. The original fan was long gone when I purchased the car.

This is the second time i've heard a lean condition can cause this, i'll double check the vacuum readings tomorrow & double check the carb. it is a 600 Holley double pump.

& yes, it overheats to 230 degrees in a couple minutes if you just idle the engine at 2000 rpm's.