Mcmillan used to offer a thumbwheel adjustable cheek piece years ago. I don't remember seeing it offered anymore, but it might still be there if you were to check. The older adjustable thumb wheels and saddles on Mcmillans were pretty notorious for coming loose after a couple dozen shots. I still fight with mine on one of my FN SPRs.
That looks like the A2 stock. It should have been the A4, but Hollywood...yet they got the optic correct for a 1999 - 2003ish (I'm not an expert) M40A3. There's too much "belly" to that forend to be an A3.