Hi Jack: i did that several months ago with my 1959 Bugeye. I called the FL DMV, told them that I had a "barn find" that had a bill of sale from Texas but no registration or title and they sent me the paragraph in the regulations that laid it out. I can't recall the specifics right now, but there were 3 options to get the car registered: Either (1) a title, (2) a bill of sale and an affidavit from the owner that there were no outstanding leins on the car, and (3) I can't remember exactly but maybe a bill of sale and registration. I did option 2 and did not have any problem.
I just found what the DMV sent me:
Section 319.23(3)(a)(2)(c), Florida Statutes, reads: “If the vehicle is an ancient or antique vehicle as defined in s. 320.086, F.S., the application shall be accompanied by a certificate of title; a bill of sale and a registration; or a bill of sale and an affidavit by the owner defending the title from all claims. The bill of sale must contain a complete vehicle description to include the vehicle identification or engine number, year make, color, selling price, and signatures of the seller and purchaser.”