Any links or recommendations on the upper/magazines.
I'd do a search, or wait for one of the experts to chime in here. Like I said, I'm no expert, and I might give some bad advice. I have a Rock River AR with heavy target barrel and shorter tactical type. Both .223. I'm very happy with their quality and service.
People that sell the uppers sell magazines. There was also a company that was making a modular lower AR receiver that could be adapted to different magazine wells, one of which took AK-47 magazines. Not sure how that worked out.
Wouldn't depend on the caliber but the make of the weapon as to what type magazine you could use. Lots of stuff out there for AK/SKS type rifles, ranging from decent to gawdawful. Couldn't tell you which was which.
Mine is a Ruger Mini-30, for which I do have some high-capacity magazines, of uniformly decent quality, and weren't difficult to find.
the infowarrior