Where do you live? In KA rifles have to have an OAL above 30" I believe. To get around this, most folks attach a fake can to extend the OAL.
Someone else feel free to chime in but I don't believe you'd ever be able to register an AUG or Tavor as a pistol because of the stock.
Now that I think about it, its not what you want to register it as but what the dealer sells it to you as. I.e. AR and AK pistols are sold as pistols sans stock from the dealer and they are noted in the books as such. I don't think you'll find a dealer that would be willing to sell an AUG or Tavor as a pistol.