3 shot burst conversion possible?

[Robb Jensen]

See Here

Regardless of the name of that site there are no class III guns, there are FFL/SOT holders (some are Class 3 dealers) who can deal in Title II NFA firearms. Guns themselves are either Title I or Title II.

From the web site you posted the link to:

What are NFA Weapons?

There are two kinds of firearms under U.S. (federal) law,
title 1 firearms and title 2. Title 1 firearms are long guns
(rifles and shotguns), handguns, firearm frames or receivers, and
most NFA weapons are also title 1 firearms. Title 2 weapons are
NFA weapons. Title 2 of the 1968 Gun Control Act is the National
Firearms Act (26 USC sec. 5801 et seq.), hence NFA. Title 1 is
generally called the Gun Control Act, (18 USC sec. 921 et seq.).
NFA weapons are sometimes called class 3 weapons, because a class
3 SOT (see below) is needed to deal in NFA weapons.