The basic pistol grip conversion is cake. The SBS process....not so much. You'd have to be damn good at TIG welding, as well as having a lathe and such to shorten the barrel and also the gas system, which looks like a bitch to do from my point of view.
The Tax Stamp, is a stamp on a piece of paper (form 4) that is required for all NFA items.
The process goes like this:
-You find a gun
-If you're doing the conversion yourself, you send out a form 1 to the ATF with all the needed info. Wait 3-6 months for the ATF to return it with a 'tax stamp' on it, and then you're clear to build your SBS. Doing so before receiving your tax stamp is a felony. You'll need to stamp or engrave your Tax Stamp # as well as some other info onto the gun.
-If you plan on having Tromix do it (I'd highly recommend this route), you'll need to get on the waitlist for the conversion. At this time, they aren't taking any more people on the waitlist, and will open up a new list starting January 2011. So you're really gonna have to wait a while. Once your # is up, and Tromix goes to do the conversion, they'll send out the Form 1 to the ATF. They'll get the form back in about 2 weeks. Meanwhile, you'd need to line up an NFA (Class 2 or 3) dealer in your neighborhood. This person will be who Tromix ships the finished gun to. Tromix will finish the gun upon receiving your dealer's info and ship it to your dealer on a Form 3. At this point, you go see your dealer and fill out a Form 4. Pay your dealer his transfer fee (around $100), as well as the $200 for the tax stamp. Wait 3-6 months for the slow ass ATF to send back your paperwork.
-Pick up your SBS
Yea........it's not confusing or complicated at all.........