Yes it would be legal with out the stock. Old G.O. from sportsman's guide can't be bothered to explain the ins and outs of creating a SBR. It is easier and safer legally for G.O. to let you think you have to use that stock and barrel together... Like I said, you can use just the long barrel but that would be stupid. (I wonder if the gun would cycle correctly.)
The barrel length isn't an issue without the stock. Follow me?
Stopping power: The power some guns have to make you stop what you are doing and get your wallet out.