One important point - the only important figure you need to keep in mind is the clearance given in the manual between valve stem and guide bore.
I don‘t know if you are using your old valves, but if you are, the the stem has probably worn off some. If you now ream the guides to the factory specs, then the clearance will be too large and not work as it should. So measure your stems, add the clearance given in your manual and this is the bore size you want to aim for with your reamer.