Wow! Applying the 'repurposing' ideas from your last video - good call! Think I saw a sneak peak of an LBV-88(?) while you were checking fit on the ALICE 3-mag pouch. I can actually fit 3 PMAGS (5.56) in those if you flip one upside down.
I use standard 3 mag M-16 mag pouches for my .308 rounds used by my M1A/M14 rifle. You can only load 2 instead of 3 mags, but no big deal. The old M-16 mag pouches are great, cheap and plentiful. FYI: I talked to soldiers coming back from the sandbox and the only thing NOT jamming was the M-14/M1A and MG240B chambered in .308. The AR platform jams now, jammed when they first introduced it, and now thankfully being replaced by the Sig Spear. The Iraqis would wait for a sandstorm to attack because their AKs worked fine in sandstorms and US troops had to use etools to fight against machine guns. An M4/M16 will get you killed in my opinion. Stick with something reliable and can reach out to 600 yards. I do.
I hunt with a FAL, a 308 /762 NATO caliber rifle, I can put two of those 20 round FAL mags int a 3 mag M-16 Mag pouch. I also took a 100 round saw pouch, fastened the sides down and can fit three FAL mags into that pouch.