Well from everything I've read it gets into one of those situations where you'd be taking a chance to do it yourself. While the final result will not be an SBS, during the process i.e. after the barrel is cut but before the brake is permanently attached, it is an SBS. Or, I assume if it were ever known (by the ATF) that you did the work yourself the assumption would be that at one point in time if only for a few minutes it was an SBS or you created an SBS without being licensed to do so.
I know it may seem overly paranoid and the chances it would ever come to light (like getting into a 922r beef) are slim, but most advice I've ever gotten has been to have the right person do it and avoid even the slightest chance of a problem.
Getting a stamp is another way but the money, time and hassle of going that route isn't attractive to me, especially when the final product is going to be a legal, 18+" barrel.
Oh, and I don't hate on the SBS guys, I'm happy for you. I'd love to shoot them sometime. I think if I were going to go the stamp route I'd get a can for my P220, but that's just me.
Someone mentioned the engraving and such, that's another reason I'm not wild about this, having to set up a trust and from what I know if you want to take the weapon over a state line you have to file a form with the ATF. All my "kin" is in North Carolina and I have nephews to are gunners. I'd hate the idea of having to do paperwork to go home to shed some lead.
And another thing, in this post I'm also asking about machine work other than the barrel etc. so if anyone knows of a good machinist, chime in.