I used the G26 to measure my dimensions. I had it marked off with Sharpie for a while before I decided to take the plunge.
I'd say "What if you mess it up?". Then I'd say "You can do this, it's not that hard." One afternoon I just went for it. I cut a little above the lines I had marked and filed down until I was where I needed to be, File a bit and measure.
If anyone has any doubt about doing it yourself, Cope Reynolds at the above website does an excellent job. And they do stippling and other gunsmith work, too. Go there and look at the pics.