Hans Monk Had A P-50 Witha "MIXER BOXER"
As I recall, the external rotary valve make people think is was a "RACE" motor. Hans Monk had a "MAY TAG MOTHER" with a "Mixer Boxer" (External Rotary valve)....with lots of POLISHED METAL...But is was a P-50...
External Rotary Valves & Racing Gear Cases
No, Ron , external (i. e., gear driven) rotary valves were on all S, P, V and X engines from 1929 through 1936. That's 20, 30, 40, and 50 ci.
And, Matts, there was really no difference in the power heads (to my knowledge) between the P45 through P80 and the PR55. The Ps had a muffler. They both had a one inch upper journal on the crank and bronze bushings.
The PR55 had a short tower housing and a PR55 foot. They both were 12:21 gear ratios and they both had essentially the same parts. The upper half of the unit of the PR55 was more streamlined and had no exhaust inlet place.
Now, the PR65 had almost no interchangeable parts with the "fishin" motors.