Piston: JE or Wiseco..........go with a .20 or .40 over-bore, 10.5:1 or stock compression and you can still run pump gas
Cam: Hotcam, webcam, powroll, megacycle........you'll be happiest with a .390 or comparable setup
Cam Chain: DID or factory oem
Springs: Kibblewhite, Versha, Trinity.......get HD springs, ask if it is not specified, OEM tension is to light.
Gaskets: Cometic or Versha.......these kits will lower your deck height slightly which will add to your HP gains
(all those are major companies, Google them and get there websites, or ebay for parts, if buying used, look for low hour parts)
The bore and hone should be done by a specialist, call around locally and look for a specialized engine builder or ATV mechanic shop. If you can afford it, get a P&P done as well or at least get the head cleaned/blasted.
You might want to also think about adding a oil cooler (big bear or clutch cover mod) and a new clutch or add a plate
{{{Damn I'm good, I just built a bad ass 350 engine in about 5 mins
}}}