Seems like you really have made a mountain out of a molehill there Brian! Mind you with all those facilities....... We often used to encounter sheared-off spigots from the front pads of L42 rifles caused by the additional rotational forces of the 7.62mm rounds against the moments of the bracket. Just insert an accurately made sleeve into the front pad as illustrated in the little H&H book and this will cure your need for the shell mill cutter. The perfect fit of the pad spigot into the corresponding opening in the bracket is critical for one of the woprkshop inspection stages.
Make sure that you read up on the article about making up a decent repro No4T too