Sorry for my short answer before 0utlaw.

So two routes I know of for SBR manufacture. Buy a rifle and send the paperwork off, when its approved send to be cut. On AK's this is a little harder than on AR's as you usually need a different gas block and such, depending on how short you go. The other way is to buy a pistol and send the paperwork off, when its approved mount your stock.

(I'm skipping stuff like engraving, but you get the gist).

I chose to go the sigbrace method. ( http://www.jgsales.com/sb47-stabiliz....-p-65088.html ) because then I don't have to deal with the ATF and taking out of state (say to deer camp) doesn't require me to file forms.