There's really only one version of the F. There were several - 3 - versions of metered prisms, the FtN is the last and best IMO. BUT - the potentiometers wear and get erratic. They all can be calibrated to use silver oxide cells instead of mercuric (unavailable) oxide cells. My favorite is the plain non-metered prism, but these alone can cost as much as a nice body and lens.
Originally Posted by CuS
Any F will be at least 39 years old, plan to have to pay for a CLA on anything you buy. They're great cameras, one of the all-time finest SLRs ever made.
Don't forget to get a 105/2.5 Nikkor as well.