I did the research on the tag you are talking about and you actually have to apply to Tallahassee to get that antique/horseless carriage status. If you use it outside of parades and exhibitions it will just be a matter of time before youl get a ticket.
If you are wanting to save a few dollars on registering your truck in Florida, this is how I would do it: 1. Bob it like you suggested and then take it to any weigh station (truck stop, concrete company, etc.) and have them issue you a weight. Them take that new weight in and register the truck on that baisis. 2. When you go to register it they will ask you what GVW you want. Tell them you want 1,000 pounds more than the net wieght. So, if your bobbed duce comes in at 11,000 pounds net and you ask for 1,000 pound weight, your GVW will be 12,000 pounds. That will come in at around $120 per year to register it. You could of course ask for more, just be prepared to pay for it.
Alternatively, if you bring it in as a 6x6 and register it at it's full capacity, you might end up paying annual tax on 24,000- 30,000 GVW which will cost a lot every year.
If you do register it at 12,000 GVW, you are agreeing you won't carry more than that on road. This route will cost you more than the antique plate, but you'll not have to worry unless law enforcement seriously chanllenges the weight of what you are hauling compared to your GVW.
As for the inexpensive collector insurance designed for parades, it is good for that. However, if by chance you are in an accident unrelated to the parade, they will not provide coverage or a defense and then if the other insurance carrier pays, they will follow you around forever trying to get their money back which could include collections, suits, garnishments, etc. For my Unimog, I pay $320 per year for 100/300/100 for convential liability coverage and $76 per year registration and I never worry about the whirling red lights following me.