You will not be able to see any iron sights with your ACOG mounted in any way unless you mount it to the top of a carry handle. If you are mounting the irons to an ACOG mounted directly to the flat top, you need a folding BUIS that will fit under the ACOG. The only way to use it would be to take the ACOG off, and then flip up the sight. Having said that, I'll copy and past something I just typed like 10 minutes ago in another part of the forum.

Most folding BUIS's fit under just fine. If using the supplied TA51 ACOG mount of the RCO or TA31f, the ARMS #40 may or may not fit. For some reason, some do and some dont. I suppose its just the varying tollerances between the eye piece of the ACOG, height of the TA51 mount, height of the BUIS and who knows what else. I just know sometimes the #40 works, some times not. If you want a sure thing, go with the ARMS #40L, Troy BUIS (like in my pic), Matec, KAC 300M (probably the one most used in the military) or the KAC 600M, GG&G A2 or GG&G M.A.D.. There's probably more, but the above 7 choices are all top tier.

+1 on the Trijicon rear tritium. The rear sight is so close to your eye that the rear night sight doesnt do anything at all.

Also curious as to why you chose the GG&G ACOG mount? I have not used one of their acu-cam ACOG mounts, but have used their acu-cam EoTech mount. It came loose once and we're currently questioning its ability to hold zero. Have you seen any of the other ACOG mounts available before you made your choice?