The angle of the photo is trollery. They are just as banana'd as any other 7.62x39mm AK-style. The reason for the curvature lies within the design of the round's casing - it tapers down slightly towards the neck. As such, the rounds were incapable of stacking straight like 5.56x45mm (AR-15) or 5.45x39mm (AK-74) could, for example.
Why the tapering? More reliable stripping and chambering of the round, better extraction at low pressures and in adverse conditions, and steel casings (what was used back then when the brass was reserved for other uses) expand too much.
Just go with AK-74 mags but pull out the internal assembly, tighten the screws, and use tightly-wrapped electrical tape on them
cheers!