While I appreciate good craftsmanship, and a desire for perfection, I don't think we need to go overboard on this hole. This is a pin joint, meaning it does not handle any of the bending loads. All the bending loads go through the front spar. The rear spar joint only handles torsion loads, such as are created by the airfoil's pitching moment, and/or flap deflection. The NACA 23000 series airfoils were specifically designed to have very low pitching moments. The result is that the loads on this joint are relatively low. I read a story about an RV-4 that flew for some time with no bolt in the rear spar attachment at all, due to a builder screwup.
So, pay attention to edge distance. Properly torque the bolt. But there is no need to go to the lengths of using close tolerance bolts, reamers, etc, in my opinion (worth what you paid for it). If there was, Van would have specified it on the plans or in the instructions.
If you do use a reamer to get a close tolerance, how much clearance should you leave for anti-corrosion primer? Corrosion is probably a bigger long term risk than a too loose bolt.