Hello & Welcome
The best way would be with a mill, I remember someone did one with a dremel & file already but I think that would be up to you to decide if your skill level will allow this.
You might want to ask at local machine shops too, some will do it as long as you give them all the info needed.
I know I seen the info on here before, see if you can find it, I'll check back and see if I can help later.
Off the top of my head for someone to do it, look for restoreit in the classifieds, he offers services.