Valves: There are a mob in the US (ebay) that sell oversize valves and guides. They have a really good rap with the honda guys, and they are CHEAP in comparison to everything else. I would go them
Bearings: King or ACL. No downsides to going oversized bearings (undersized journals).
Headgasket: Various companies offer an "83mm" bore headgasket for 4A motors, which is probably what you'll need to use.