as long as you put enough american parts in it to keep it 922(r) compliant there shouldnt be a problem. american companies are the ones that make the single stack, low-cap versions into double stack, high-cap versions after the guns are imported as low-cap( and century does a horrible job at it, look at some of the other wasr-10's).
i believe you only need 5 parts to make it legal
U.S. made FCG(hammer, disconnector, trigger) (3)
Tapco furniture(made in usa of course, butt stock, pistol grip,hand gaurd) (3)
6 parts. legal. pistol grip and buttstock you can get way cheap (mine combined were like $60) but the hand gaurds a little more expensive depending on what you get.
i did it to my wasr 2 actually. its pretty simple, just take your time and go slow. grind it instead of cutting it. easier to check progress and make adjustments.
GunCentral.net - WASR Mag Conversion
thats the site i used for a guideline.