[blue]      (7) The term ''rifle'' means a weapon designed or redesigned,

   made or remade, and intended to be fired from the shoulder and

   designed or redesigned and made or remade to use the energy of an

   explosive to fire only a single projectile through a rifled bore

   for each single pull of the trigger.

     (8) The term ''short-barreled rifle'' means a rifle having one or

   more barrels less than sixteen inches in length and any weapon made

   from a rifle (whether by alteration, modification, or otherwise) if

   such weapon, as modified, has an overall length of less than

   twenty-six inches.

(29) The term ''handgun'' means -

       (A) a firearm which has a short stock and is designed to be

     held and fired by the use of a single hand; and

       (B) any combination of parts from which a firearm described in

     subparagraph (A) can be assembled.

(30) The term ''semiautomatic assault weapon'' means -

C) a semiautomatic pistol that has an ability to accept a

     detachable magazine and has at least 2 of -

         (i) an ammunition magazine that attaches to the pistol

       outside of the pistol grip;

         (ii) a threaded barrel capable of accepting a barrel

       extender, flash suppressor, forward handgrip, or silencer;

         (iii) a shroud that is attached to, or partially or

       completely encircles, the barrel and that permits the shooter

       to hold the firearm with the nontrigger hand without being

       burned;

         (iv) a manufactured weight of 50 ounces or more when the

       pistol is unloaded; and

         (v) a semiautomatic version of an automatic firearm; and[/blue]

You can have a longer barrel on a pistol but when dealing with AR pistols you are still governed by the AWB.

I am not sure if the alterations you mentioned would be enough to make sure your lower will be exempt from the AWB rules. I assume you have checked into all that already?