Been there, done that. You will need to replace the valves (why not?), guides (for sure) and seals (for sure). There is no reason, in my mind, to have the head off and do work, without replacing the guides and seals. F2 heads are notorious for EATING valve guides. Mine had 10,000 miles on them and I could almost fit 2 valves through there. I'm not even kidding. If I were you, I'd send the head out to APE (look 'em up. they are in Rossville or Roseville or something like that, CA), along with the parts. Let them totally strip the head down and rebuild with new valve seats cut and guides inserted. If you want to spend more money, let them port the intakes. As for cam choices, the F2 is fairly radical to begin with, much more so than the K. I'm not sure how much more you'll get out of the Webcam 41. I did the research, and couldn't determine if it's even "hotter" than the stock F2, which you never get accurate apples to apples comparison numbers on it, in terms of duration and overlap.
Rings: rings are considered impossible to get; but, I know a guy in the UK who does sell them, and they will fit the F2 pistons. So, the K and F pistons are different. The rings are not interchangeable. The good news is that the rings and bores on the F2 are generally considered to be bomb proof, and will not wear until 50k or higher. Mine were nearly new when I had them checked.
Have fun.
