1) there is no such thing as a "class 3 license" required for an individual to own title II equipment.
2) the upper reciever for an AR15 is not a firearm of any sort, it is just another part. the firearm is the serialized part.
3) the only way the "auto" upper would do anything different for you is if you already owned an M16 or a conversion device, all of which would have had to be made and registered in the NFARTR *prior* to may of 1986. on an AR15 lower, and "auto" upper won't do anything different then a semi-auto upper.
4) a machine gun is a machine gun, regardless of caliber. if you could just get around the NFA by using .22, everyone would own .22 machine guns.
ETA: beaten by 47 seconds.