RE: Jett .35 RPM range (new)
You should not begin with a 9x6.
Put it on a good test stand and follow the run in instructions. Prop for this should be one size smaller diameter.
if it got lean and hot be certain to check the head bolts before you install a new glowplug.
Start there. Do not get it lean. With breakin prop the engine should get to 17500 while still rich.
Bob