Best bet is to buy the jig that Brownells sells, and drill and tap in a drill press with a machinists vice. You should carefully level the drill press/mill, then the vice, the jig, the part, etc. with bubble levels. When you've done it for pay, you start looking at the work of others, and you start noticing, "Hey, that sight base is ..a..little off"
Things like this, where you have to buy a jig to do a decent job are, in my opinion, best left to the competent smith. He's (hopefully) got the tools and training to make it happen.
I would take this opportunity to strike up a relationship with your local 'smith.