Saiga rifles don't have an AK bullet guide, that's what keeps the mags from working, install a bullet guide and you can use the AK mags. The stock has nothing to do with the mags. The stock shown doesn't require any conversion and installs in minutes. If you want a true AK look, you need to move the trigger forward, as others have said, I would use a conversion kit. It sounds a bit overwhelming, but from what I hear, even a beginner can do it.
Arsenal Inc. converts them for sale, but they go for between $800-$1000. Convert it yourself and save a ton, It doesn't get any cooler than a Russian made AK.