There is no such thing as a C172 type rating. If you have a Single-Engine Piston Class Rating, you are qualified to fly any SEP aeroplane - C152, PA28, etc. with no other training required. If you wish to fly an aeroplane with VP prop, rectractable gear, tailwheel, etc. you will need differences training, which should take no more than 1 hour and which must be signed off in your logbook by an FI.
Does a C172 have a VP prop? - all these puddle-jumpers look the same to me.