Jordan: What are you doing with Boys mags.....Best you save yourself a lot of money and sell it to me. That way you will save a small fortune not having to buy the rifle, and another small fortune not buying the ammo.
Below I checked the size with a Boys mag and a Bren mag on top of one of those rusty metal plates. Looks like a precise fit.
If someone has a good example of one of these pouches available for loan, I would be willing to make up some pretty exact copies.