Drilling the bolts compromises the strength and integrity of the bolt.The amount of flexing that I have seen in shafts,stands and the entire Hemi valve train and the harmonics under extreme loads would want me to consider outer methods like the oiling chambers on HemiFreds car or just make the original design work more efficient.We have never had to custom build a rocker oiling system on any Hemi,we just improve what is there.Sometimes we have had to modify after market rockers and shafts by drilling better oil holes and channels.