The mag I measured was an MDT. I eventually found an AICS mag from Accuracy International with internal dimensions that would support a 2.880+ O.A.L. so that will work fine.
I'm hoping that the high rings on the NightForce scope with the 56mm front objective will get the optical axis high enough to let me get behind the scope comfortably.
If not, I will have to find some extra high rings and they will be expensive.
I expect to try the Oryx stock on my 12 FV 6.5mm CM shortly.
We'll see if the sturdier, less flexible stock can outshoot the cheap factory plastic stock.

I have a set of extra high rings on the way for my .223 so I can try the Oryx on 12 FV .223 with the 36X42mm Sightron scope. I'm hoping that will make the optical plane high enough to get behind the scope. Medium high rings that shoot great on the 12 FV factory stock were way too low ion the Oryx.
Fortunately, the AICS magazine for the .223 has more O.A.L. space than I could ever use.
Even a 77 gr bullet would be out of the neck if I ever loaded it out to the end of that mag.