I would assume that this situation would be similar to the suppressed CCW question - provided you got the tax stamp for the weapon and had your CHL, I suspect it would be legal, though you would definitely be treading in a very, very grey area.
Why do you think you would need a class 3 license? Do you intend to sell full-auto Glocks, too?
Full auto would be a bad idea, IMHO, but a 2 or perhaps 3 round burst could be practical.
Oh ya - don't forget that your life would be virtually ruined if you ever had to use the thing. Everyone remember the story of the HK employee who used a full auto Ruger (i think?) on a couple of bikers who were trying to kill him and his family? That guy spent many years in court and H&K's financial backing was probably the only thing that saved his children's college funds, not to mention everything else of any financial value he owned.