Life Imitates Art: It's unlikely if Mel Brooks knew the story, but in Real Life, a black man was named as the postmaster of Punta Gorda, Florida by a man who held a grudge against the town's founders, as a deliberate affront to its Southern sensibilities.
Brooks wanted John Wayne for the role of Jim. Wayne rejected his offer because the script clashed with his family-friendly screen persona, but he also found it to be hilarious and told Brooks he'd be "first in line" to see the movie.
Had Richard Pryor (who contributed to the script) been a more reliable actor and/or not coked out of his mind (Mel Brooks found out the truth of the warnings he'd been given when Pryor called on a day he was supposed to be writing to explain he was actually with a couple of girls in New Jersey), he would have played Bart himself, launching his frequent film partnership with Gene Wilder a couple years before Silver Streak.
Wilder himself was a last-minute replacement for Gig Young, who turned up on the set too inebriated to act. Several other actors were considered before Young.