After much searching, I finally found a factory-style thermo-mechanical engine cooling fan. This is better than an electric fan for all but the most highly modified cars, especially when there's an air conditioner to be cooled also. My problem was that this engine has a reverse-rotation waterpump because the back side of the belt turns the pump pulley. The only vehicles that use this engine with a mechanical fan are the Chevy and GMC trucks, and their fans are way too large to fit in this car's radiator shroud! Finally I found just what the Dr. ordered. It is from a Chevy Astro minivan. The Astro has a 4.3 V6 with the same reverse-rotation waterpump as my 305; and it has a small radiator. This fan does no better than the huge PWM-controlled electric fan I had- but it saves lots of electrical power and removes some clutter (control module) from under the hood. Let alone being simpler and more reliable.

Just barely fit in the shroud! In fact, I had to notch the bottom of the shroud slightly. It's about 0.5" larger in diameter than the original fan.