I believe John Chenery ran his engine with a 20x8 propeller and saw 3000+ rpm.
When purchasing a propeller be sure to check hub thickness and diameter. In my experience many are much to thin to use with fabricating spacer(s). That would look odd, in my opinion. Also, be aware that with the proliferation of electric motor used in models you may come across props that are fine for electric but not suitable for IC engines. It's best to stick with out fashioned wood.
One potential source of good quality propellers is Falcon but I'm afraid there are inventory issues with the vintage styles. I've no connection with them; only a satisfied customer.
What could look better on your vintage plane than one of our scale-like vintage props. Designed to look period appropriate and delivery great performance.
The Civilian Style Propeller is an ideal compliment to any Scale plane e.g. Cub, Stearman. These Props are modeled on post 1950’s style Propellers.
Yes, prices are like buying groceries ... but still beats starting with a length of lumber and a sharp knife.
Regarding the cam design, I haven't run my Anzani yet but did build the cam to drawing. I'm pretty sure the duration will work out fine. The duration may seem long on paper but one mustn't forget that the piston doesn't move very far around top and bottom dead centre for a given crankshaft rotation. We'll see once I get the oil and fuel tanks finished and mounted to the stand ...