Holden 202 Valve Stem Guide Seat Cutting For Viton Seals 

This will show you how to cut Holden 202 valve stem guide seats to fit modern day seals.
Head valves are typically of 11/32" in size, so this may be the arbor you'll want. Common cutter tool size is 0.530". Make sure you get a set of vrenier calipers and do your measurements before proceeding. Advantages of having this mod done is longevity of the valve stem rubbers, which will mean your engine isn't likely to burn excessive oil and foul up plugs etc, through too much oil bypassing through the valve stem guides.