Go to the local tag office (county tax collector) with a photo of the tag and explain the whole situation and your desired outcome. Typically they will make it very simple for you.
Florida does not issue titles under a certain weight
, which you can find out during your visit. Good to know the weight
if it is placarded, otherwise take it to a scrap scale and tip the guy for a weight
Here in Broward County the tag offices have receptionists who are generally quite knowledgeable, and save you a bit if wait. They also will provide you with all the forms, and instructions. Be ready to take notes. Pretty much everything can be done without bringing your neighbor in - there are powers of attorney, transfer papers, bills of sale, etc.
What I did with the last "seller absent" auto purchase was to get all the forms from the receptionist, with required fields highlighted, then search online for the PDFs, type the info into the blanks, and have a good readable copy to turn in. Your handwriting may be better than mine.... :-)