the mags between the 47 and 74 are not interchangeable, the 47 is wider and shorter than the 74, the 74 has a longer projectile, less case taper and narrower case head.
tapco makes a decent mag but the bulgy, east german and polish mags are simply the best and so are the soviet if you can find them.
I buy all my Ak stuff at www.K-var.com
good luck