Oh man a jig would be so much easier. I did the hard way using the TLAR method (That Looks About Right) and then measure it, not a lot of room for error. I did mine on rifle so it was relatively easy to check though. And it was pretty straight forward, i.e. cut it off, trim to height and weld it on, the worst part was getting gumption cutting it off the perfectly good Saiga to start with.
1st I did on a Saiga
This is one I did on a Romy G build.
Needless to say, it works and looks much better on the straight rather than the sloped style gas blocks.