I think you're talking about the Blindhogg site. He uses a milling machine to get a precise cut. If you are really focused on a perfect cut, send it to Evolution Gun Works and they'll blend it for $30. Of course, shipping the frame can get pricey.....
I can post pics of mine, but it looks a lot like Blindhogg's save that I opened mine up a bit more.
Depending on your 1911, there is usually a small bevel in the mag opening machined into the frame. I just filed away on the S&A magwell until it matched that angle. I don't like taking metal off the frame of the gun, but some people open them up as much as possible.