What does the "P" and the "PF" mean, and is there any significant visual difference?
Variants I know of:
Mig-17 (Fresco A)
Mig-17F (Fresco C) - different engine with afterburner
Mig-17PF (Fresco D) - added radar
Mig-17PFU (Fresco E) - cannons deleted, 4 AA missiles instead
List does not include export variants (S-104, LIM-5M, LIM-6, LIM-5P, J-5, and J-5A).