I did mine, but with the Bulgarian version. Cutting the rear of the receiver was rather straightforward - it's just a tad scary when you actually start the cut. I found that the Bulgarian rear trunnion needed to be thinned a few thousandths to fit properly on account of the the thicker receiver on the Saiga-12. Two sets of holes for the rivets are already there and line up perfectly. You'll only need to drill the lowest, rearmost one. I welded shut the orginal trigger holes.
The front latch was the most difficult part because there isn't enough room between the front trunnion and the receiver for the latch and its accompying hardware. I had to thin the latch hook internally, then modified it so I could attach a spring.
That's a drawing of my latch mod. I welded an extension to the latch. A spring goes into a hole drilled into the extension. The other end of the spring goes into a recess drilled into the handguard - kind of a hack, but it works.