Valve guides have to be cold pressed in and out (not something you can do at home) and valve seals are just the little rubber cups that attach to the end of each guide the stop the oil from leaking back into the combustion chamber. If you're worried about the valve guides themselves being worn, then there is a good chance that the valves too may also have experienced some wear as they tend to wear a patter of the individual guide they belong to. You’ll probably be fine though, as the valves themselves are made of a harder material than that of the guides, but it’s fair to mention this just in case. Your machinist will only know for sure if there is any noticeable wear. Valves, valve guides and valve seats all come in a variety of materials. You can get the valves in a standard hardened steel, as well as stainless and titanium. Guides like the valves themselves also can be chosen based on the type of duty they’re going to see and are unusually of the standard iron, or brass variety. Seats are the same with your standard hardened steel or nickel bronze variety. Unless you engine it going to be seeing some serious heat and/or high RPM track duty, the standard valves, guides and seats will be more than sufficient.
As far as the valve job goes, assuming that the heads are original, you can probably just have the valve seats themselves reground along with fresh faces cut into your valves. Grinding valves and seats is kind of an art form and there are many different methods and combinations of angles that different performance shops like to use. The 3-angle cut is standard and will be what you want if you're going with any sort of power adder, but if you want the best out of your N/A combination, springing for a 5-angle job is the ticket. You could go with the 5-angle job with the power adder too, but you need to keep in mind that the valve seats themselves are going to have narrower face areas when more angles are cut into them and as such may reduce the longevity of the valve job when in combination with the elevated cylinder temperatures that Forced Induction or Nitrous Oxide will bring to the table with them.
What’s the mileage on the heads? You won’t know until you get them apart, but if there is no major pitting on the valve faces themselves, then you may just get away with a fresh “lap” to restore their lifespan. Modular heads don’t often experience major wear on the guides or the valves themselves in my experience, because they don’t have the high ratio rocker angles that a lot of the OHV engines do, so you’re likely to be able to get buy with just the valve job and some new seals….but again, only your machinist will be able to confirm this for sure.
