To answer one of your questions, the counterweight on my 56 235 is on top of the shaft when in the heat on position (cold), and rotates toward the engine when things warm up. Mine was stuck in the heat on position for the first 3 years I have owned the truck, and I have not noticed any difference in how the engine runs with it now working. I did have a problem starting when the engine was hot that I think might be related to the valve, I will see how it does this summer. I think your issues are someplace else other than the heat valve.
Lee.
