Re: which mcmillan
If you decide to go with the adjustable cheekpiece I would STRONGLY recommend to ask for Terry Cross' hardware [KMW Precision]. I have used both the original McM types and Terry's version is so far ahead for solid lockup that doesn't slip that I wouldn't go any other route.
When you call McM you might want to ask for Dick Davis and he can explain more.
Wes in AZ