Apologies on that, something got crossed, yes.
Anyway, you can build a pistol from a new receiver. It's not ever been built. My point on the whole thread was, according to what I've been told by several people from ATF, two in person, two online, once a gun has been built as a long gun, shotgun or rifle, you can't make it into a pistol. You can, however, go from pistol to rifle and turn it into a long gun and then back to pistol. Why that would be different from just going from rifle to pistol is unclear to me.
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The important phrase there is right at the start, "Assuming that the firearm was originally a pistol..."
This is key to the discussion about going from rifle to pistol being illegal.