RE: Regarding SP series engines, props and airspeed...
Michael:
Unfortunately I have no records of the RPM I got (this was 3 years ago), but as far as I remember it wasn’t much different than the RPM I used to get with the APC 3 blade prop (15.75 x 13).
I hit a tree with my plane and since then the engine is stored for a future use.
I think you need at least 12 in of pitch to make this Mustang fly.
Arruda