My machinist used a Comp Cams 4716 cutter to enlarge the valve spring seats for the beehive valve springs and reduced the O.D. of the inner spring locator boss. The tool cuts 1.320" O.D. valve seat x .630" valve guide boss. The Comp Cams 26918 valve springs are 1.310" O.D. x .885" I.D. at the base. The engine builder may have used Goodson tools but they cut the same dimensions as the Comp Cams cutters. I talked to the machinist about reducing the O.D. of the inner spring locator boss and he seemed to think reducing it to .630" O.D. for the .885" I.D. valve springs would not create a problem. The cutter provides spring clearances of .005" outer x .128" inner in order to register the valve spring properly on the head. That stabilizes the valve spring and prevent "dancing" (oscillation).
The valve guide itself was cut for Comp Cams 518 Viton metal body seals for 11/32" stems (.530" guide x .575" O.D. seal) using a Comp Cams 4726 guide cutter. I think the machinist removed about .150" guide height for .060" minimum retainer to seal clearance. He used the Comp Cams Viton metal body seals on the intake and exhaust valves. The Comp Cams seals are .575" O.D. and were pushed down on the .530" guides. That places the seals .060" from the ledge of the .630" O.D. guide boss.
IMO, there is no way to avoid cutting the inner guide boss when machining the spring pockets for larger O.D. valve springs.
As I recall, the machinist may not have used the Comp Cams 614 +.050" valve locks on the exhaust valves. I gave him a set to use if he needed them after eliminating the exhaust valve rotators. I recorded most of the engine assembly data on my computer for future reference in case my memory fails me.