I think it's really an 8-36 pitch (not too common) and it was probably my post that led you astray! If you're going to file it I don't think it'll matter much. Just trim it down and bevel the edge slightly. Using a grinding wheel is where the nut pays off because it gets hot enough to warp the threads. As long as it shortens it and works for your zero it shouldn't be a worry, no one will see it buried in the sight post well anyhow!