Agreed! contender, taurus and a couple of other companies make 45 LC/410 pistols. The problem would be going from a rifle/shotgun to pistol as it would change the status of the gun to either a SBS or SBR, however going from a pistol to a rifle is no problem.
I have a 30 cal browning that I built and marked as a pistol, ever see a beltfed 8mm mauser pistol with a 9 inch barrel

Definatly not a one hander. Incenidentally, a good friend of mine is working on a bolt conversion for the 1919a4 to convert it to .410 shotgun. It will be the first beltfed .410 that I know of....
AOW transfer is 5.00
SBS/SBR transfer is 200.00
You can build it yourself and register it on a form 1 or if it has been built by a manufacturer its registered on a form 4.