The O.S. nomenclature for pull-start engines has an "X" as the designator. A "(P)" means the engine is equipmmed with a pilot-shaft type of crankshaft.

The pilot shaft is the way to retain the clutch/flywheel assembly, and has nothing to do with a recoil starter. European R/C cars tend to use the pilot shaft crank, as to a few of the Japanese R/C cars.

The O.S. Max RZ-series cannot be converted to recoil starting.

The .21 RZ has two versions, pilot shaft and non:

OSMG2065 13860 .21 RZ-V01B
OSMG2066 13861 .21 RZ-V01B (P)