[drolston]

First advance your timing a bit at a time, until the engine pings while accelerating hard in second gear, then back off a tad to minimize or eliminate the pinging.

Next step would be to do a thorough flush with one of those products that you drive with it in the system for a few hours. Then consider that in 1936 people used alcohol as antifreeze in winter and it mostly all evaporated out during the summer, so they were running straight water. 50/50 glycol based antifreeze costs you about 17% of your cooling capacity, so when you refill after the flush, use maybe half a gallon of antifreeze just for its corrosion protection, plus a bottle of water-wetter. I bet you will find that your '36 will stay much cooler in traffic.

I had problems similar to yours and switched to Dennis Carpenter water pumps, which are advertised to improve flow at idle. Did not seem to help much by themselves, but in combination with switching to very weak antifreeze mix, I can now get stuck in traffic without blowing steam.

Like you, I am using Stant thermostats for a Subaru, with two one-eighth inch holes added to let some flow get up to the thermostat bimetal part during warm up. Tried running without thermostats, and it did not help at all in traffic or at highway speeds.