Funny, my buddy just had the same problem. DO NOT grind on the mags...not that you would, but the problem is this: Take the empty rifle and look into the mag well. Look to the rear (mag release side)inside, you will see a cylindrical bar that goes from one side of the receiver to the other, for strength I guess, rivited to either side. That is what the waffle mags hang on...and only in the SAR-1. His SAM7 and my Vepr have this piece as well, but it is further back out of the way allowing the waffles to seat in the well. The waffles work in the Saigas fine too, just for some reason, the Romanian AK's have it just enough in the way for the larger waffle mags to hit on.
Now, I do not recommend this at all, but he decided to cut that little rod of steel out, and the waffles now fit the sar1. What that will do to the strength of the receiver has yet to be seen, but he did shoot it and it worked fine. Perhaps it could be moved to another position, but why bother since all the other mags work fine. Hell, I will buy your waffles...LOL!