There are no "Class Three Licenses," but there are firearms dealers licenses (FFL) who pay an additional "Occupational Tax" that allows them to deal in National Firearms Act Weapons. To transfer a weapon that is covered under the National Firearms Act one must file the form with BATFE and pay a tax of $200.00 or $5.00 for any other weapons (AOW). Once approved the form is mailed to the current owner / manufacture who then delivers to the item and paperwork to the "new owner."
Now lets say that you have spent the big bucked to buy a 1911 that was converted prior to 1986 so that it is a transferable gun, there are NO Glock 18 that are transferable to anyone other than a dealer or a .gov agency. If you have a CHL with the SA endorsement you would be legal to carry the full auto 1911. Being a machine gun would not matter.
Why you would want to do so is a whole other question. The basics to possess the weapon, you must have had the weapon transferred to you after the $200.00 tax has been paid and you have received the approved form back from the BATFE. They are fun to play and are addictive. There is nothing like shooting suppressed machine guns or belt fed or miniguns. There is nothing like paying the bill for all of the ammunition that you will burn up.
A very good boards to ask technical questions about any weapon you can come up with is http://subguns.com/boards/mgmsg.cgi" onclick="window.open(this.href);return false; What ever you do, don't tell them that you have a class 3 license. You will be the brunt of jokes for years to come.
There really not that much mystery to it, just a few forms and $200.00, then the wait of 6 months before you get your new toy.