Scott, do a bit more research regarding your waterpump. The 67 type plates are definitely able to be “tuned”. I have it, and have done it. (Regarding the waterpump, what is pot metal?) I also successfully use a 19” flex fan. 185 degree thermostat. I’m pushing 500+ horsepower, so definitely understand your cooling concerns.

I assume you’re using a fan shroud…make sure the fan blades are 50/50 in/out of the shroud.

Do you have the radiator core fillers installed on top? What about the rubberized soft fillers on each side? I also added rubber stripping to the shroud where it meets the radiator to better route airflow. These are important and can make the difference.

Re hot start problem: I installed a heavy cable to a high torque mini starter. This solved my problem.

Good luck. You’ll get it figured out.