re: The most armed man in America

Class 3 license is a Curio and Relic license.
Per ATF 478.11:
To be recognized as C&R items, 478.11 specifies that firearms must fall within one of the following categories:

Firearms which were manufactured at least 50 years prior to the current date, but not including replicas of such firearms;

Firearms which are certified by the curator of a municipal, State, or Federal museum which exhibits firearms to be curios or relics of museum interest; and

Any other firearms which derive a substantial part of their monetary value from the fact that they are novel, rare, bizarre, or because of their association with some historical figure, period, or event.