I don't think Hesse is entirely correct, but that may be how they read the law. The following is from a letter to ATF concerning an AR pistol. It says you have to verify with the manufacturer but it doesn't say what you have to verify. It has been the opinon of many, that one simply has to verify that the new stripped lower was never made into a rifle. Certainly, a factory lower stamped "Pistol" on it pretty verifies it as such.
A call to the manufacturer with the serial number could verify whether a new receiver has left the factory as complete gun. The specific pistol receiver information is in the fourth paragraph.
You will note that this letter was written in 1992, before the AW ban. The AWB only adds the weight and flash hider and other stipulations to the building of an "assault weapon" type pistol, it really has nothing to do with the using of receiver for a pistol.
"Dear Mr. XXXXX:
This refers to your letter of October 1, 1992, in which you inquire
about the legality of manufacturing a handgun which utilizes a rifle
type receiver.
26 U.S.C. Chapter 53 # 5845(a)(4), the National Firearms Act (NFA),
defines the term "firearm" to include a weapon made from a rifle if
such weapon as modified has an overall length of less than 26 inches
or a barrel or barrels of less than 16 inches in length.
Utilizing the receiver of an existing rifle for the purposes of
manufacturing a handgun would constitute the making of a firearm as
defined above. Individuals desiring to make such a firearm must first
submit an ATF Form 1, Application To Make And Register a Firearm and
pay the applicable $200 making tax.
If an individual were to obtain a rifle type receiver that had not
previously been utilized in the assembly of a rifle, a handgun could be
made and not be subject to the provisions of the NFA. Verification
must be obtained from the manufacturer of the receiver to establish
its authenticity.
We trust the foregoing has been responsive to your inquiry. If we may
be of any further assistance, please contact us.
Sincerely your,
(signed)
Edward M. Owen, Jr.
Chief, Firearms Technology Branch"
So here is what I think you could do. Buy a stripped new receiver from one of the people who sell them. Let's say it is from Rock River Arms. Send a letter to RRA with the serial number and ask them to verify that the lower was not a completed gun/rifle when it left the factory.