If you're going to get the valve seats and recesses overbored I suggest you send the head and IM over to Extrudehone and let them do their stuff. Increasing the valve diameter does present one problem in an N/A setup: incoming charge velocity. To preserve the intake charge velocity and improve the engine's swept volume positive draw efficiency with this modification the Extrudehoning will re-chamfer the ports along the most efficient flow path according to the new port specification. Having the IM matched will only aid this further.

If you're going forced induction, you can also have a machine shop radial-cut your valves for better sealing under the greater, now POSITIVE intake pressure whereas before, the intake pressure was negative because the swept volume of the engine was like a vacuum cleaner, sucking.

Good luck!