Can't shoot gunfighter in any category other than Gunfighter or B-Western, also Wrangler is aged based, so yes, that could get rolled down to Cowboy.
when @mean gun mark mentioned 'base' categories, I am under the impression that he meant Gunfighter, Duelist, Classic Cowboy, B-Western, and Black Powder categories. Of which I'm under the impression they all are 'base' categories, that would always be offered. Yet, re reading the rule book, I'm not so sure.