That doesn't make any sense. I can have a rifle with a longer barrel than a pistol?
Pistol isnt defined in the Firearms act. Handgun is. As a pistol is a handgun... barrel makes no difference.
I could buy a pistol skorp, swap barrels and have it verified under the same frt number. The barrel combinations are only limited by how many people verify a change.
If they have a stock, why not just register them all as rifles under that frt?