This is a hard one, because there is no official "Alpha AK." It's not a weapon designation used by the Russian military, nor a production model. It's simply a nickname some people use to describe heavily customized rifles used by Russia's Alpha Group. You're right, most tend to be 5.45mm AK-74 variants, but they don't have to be, because there's no set for what's right.
There are 7.62x39mm bakelite mags made for AMK variant rifles. They're pretty hard to distinguish other than the 7.62mm variety tends to be more curved. I've not paid enough attention to the mag in game to tell if it looks right.