If you haven't purchased the valves yet, you may want to check this out. KF used two different types of valves in their engines and how they are held in place does differ. The early style used a pin while the later ones used a pair of keepers that slid into a groove cut around the base of the valve. You want the later style.
Also, NAPA sells valves that use the latest materials. The intake valve is part nbr SEP V1203 and the exhaust is SEP V959. It would probably be a good idea to replace the valve springs as well. They're part nbr SEP VS310. The valves are about $15 each and the springs run $7 apiece.
About the guides, unless they're scored, I'd leave them in place. Removing and replacing them requires a tool unique to flat head engines and KF had a special tool to do the job. It's nbr KF-27 in this catalog ->
http://www.circlekf.com/kflit/SM/kfsm550/kfsm55018.pdfThe windshield gasket is available from Rudy's KF parts at 760.789.3608. He's in California and it's best to try to reach him before noon pacific time.