Official Police designation started with Serial # 513216 in 1927. The Official Police was a continuation of the Army Special serial number range. Are you sure about the serial # and that it's an Official Police?
I have a frankengun that has a Officer's Model frame and an OP barrel. The serial # is in the 350XXX range, correct for an Officers Model but out of sync for an OP.
I have an OP, blued, 4" barrel, original grips that are are worn. I gave about $200 for it.