A 1/16" feed to the cam journals that ain't feeding anything upstairs is plenty (1/8" in the (2) that (normally) feed the heads is adequate). If starting from scratch you could drill/tap the vertical passages under the mains then install a setscrew drilled to .0625". In your case just guestimate how much of the hole you want covered/uncovered. Its worthwhile to do as cam bearings leak alot of oil & especially you are in a position now to correct it. every bit helps.