You can usually fit single AK mags into a double M4 pouch. I can easily get an AK mag in each pouch on my CADPAT vest or my CIRAS without issue.
Although I would recommend getting a MOLLE rig and some proper AK mag pouches for it. That's the ideal if you plan on running an AK. It will allow you to carry more mags more securely. And if you ever switch to a different gun down the road, you just have to get new mag pouches rather than a whole new rig.