Thanks hogdogs. I just Wiki'ed it and found same thing.
http://en.wikipedia.org/wiki/Sawed-o...n#Legal_issues
In the United States, due to the National Firearms Act, it is illegal for a private citizen to possess a sawed-off modern smokeless powder shotgun (a barrel length less than 18 in. or 46 cm and an overall length less than 26 inches)
Any requirement to have the stock LOOK "stockish?" Or would a rounded one suffice? 26" overall, though.