I'm pretty familiar with Florida's laws regarding registering vehicles as a former MV or firetruck, horseless carriage, antique, YOM tag, etc. The first three classes are non-starters IMO since you're ONLY allowed to drive your vehicle to and from displays, etc. By law you're not even allowed to drive it to get gas or to have it worked on!
IF your truck is old enough (pre-1977) the YOM tags are the best IMO. They're cheap ($37/year) and there are NO restrictions on what you use your truck for. However you may have problem if it weighs over 6,000 #s (I'm about to find out with mine!)
If your truck isn't old enough for YOM tags or Antique (35 year) or Horseless carriage (60 year IIRC) then you have to register it as a regular truck ($$$$) unless you mind ignoring the 'former MV' class restrictions. If you register as former MV (no year or weight restrictions AFIK) then tags are cheap and you're not required to display the tag.
I agree with Wikallen, use the oldest date you can get and you're that much closer to antique status.
Give me a shout if you have questions.