Jtab, 1. does the carb suck air from the cowl. If so, do you have a hole in the firewall at the back of the carb. If so I can send you a Kunkle venturi to try that will suck cool air from inside the fuse.
2. Move the prop 90 degrees. It may not be dynamically balanced. The engine is not dynamically perfect. Changing the prop position can anti phase out the vibration period. Been doing this for years with many engines. If not better do 180 degrees.
3. In my experience the fuel pump is a great benefit but on only 4.8 volts.
4. Richen the high end needle a bit?
5. Keep the top hat cool inside the fuse. Hope all helps -Tom