Open Carry is Legal, but you will end up in jail until they figure it out.
The fact that a firearm is an antique firearm is an affirmative defense to the charge of carrying a concealed firearm. This means proof of it's 'antiqueness' would have to be provided to the court.
I believe you are mistaken about the 'affirmative defense' status of Antique Firearms with regard to 790.053.
790.053
Open carrying of weapons.
—
(1) Except as otherwise provided by law and in subsection (2), it is unlawful for any person to openly carry on or about his or her person any firearm or electric weapon or device.
(2) A person may openly carry, for purposes of lawful self-defense:
(a) A self-defense chemical spray.
(b) A nonlethal stun gun or dart-firing stun gun or other nonlethal electric weapon or device that is designed solely for defensive purposes.
(3) Any person violating this section commits a misdemeanor of the second degree, punishable as provided in s. 775.082 or s. 775.083.
It has already been established in the first post that according to Fla statutes:
790.001 Definitions.--
As used in this chapter, except where the context otherwise requires:
(6) "Firearm" means any weapon (including a starter gun) which will, is designed to, or may readily be converted to expel a projectile by the action of an explosive; the frame or receiver of any such weapon; any firearm muffler or firearm silencer; any destructive device; or any machine gun. The term "firearm" does not include an antique firearm unless the antique firearm is used in the commission of a crime.
NOTE, that 790.001 establishes a SPECIFIC circumstance in which an Antique Firearm is considered to BE a Firearm. Your claim that a specific exeption must be written into 790.25 for Antique Firearms is a red herring. Unless I'm mistaken Fla operates on the English Common Law model in which that which is not specifically prohibited, is lawful.
To sum up:
OC of a 'Firearm' is generally prohibited by Fla Statute (790.053)
Exceptions to this general prohibition are listed in the statutes as well (790.25)
The term 'Firearm' is SPECIFICALLY defined FOR THIS SECTION in yet another Fla Statute (790.001)
For the purposes of this section of Fla Statutes, an Antique Firearm is expressly and specifically NOT equated to a Firearm.
ERGO, since FLa Statute 790.053 DOES NOT specifically include Antique Firearms in it's text, said statute DOES NOT APPLY to these items.
Period. Full stop. End of story.