Ray:
I don't know much about AMA classification, but in SCTA parlance, P-P stands for Production (engine), Production (bodyworks and chassis). To designate a pushrod-type production bike you'd show P-PP (production engine, production body parts, and pushrod engine).
I've got a copy of the FIM rules and classes -- but they'd drive you far more batty than you already are -- and we don't need that, do we?