I am looking at my mac now, and it appears on my Velocity Mac the sight is about 5 millimeters wide. I was going to suggest with a Dremel grinding off 2 millimeters off one side of the front sight post, but it seems this would leave little room for error (and strength).
My question is, do you have a tapped hole directly in front of the post? I do not know what this hole is on mine, but it actually appears dead center, like an actual threaded sight post can be installed here as well.