It depends on which way you're going with the build I suppose, I tend to steer away from ball and get cartridge bearing headsets. That said I'm still running a bog standard tioga in my GT backwoods because that's what came with the bike. Why not throw some new cage bearings in there with decent grease and see how it goes for a season and upgrade later?
Stout hubs on FSR's in 99/00 ran mega 9 iirc, so you may get lucky on the mega range dinner plate rear cassette ;-)