I have found no formal documentation to back it up, but as I recall, the Henry J used "Dinosaur Vinyl" and they called the fabric "Dragon" or "Dinosaur" so the public would know it was not real animal hyde. A lot of people refer to it as "alligator" but I don't believe KF ever did in any of their literature. Perhaps Jack can chime in - seems I read this in LOOD but I'm not in place where I can go look it up.
Also, even on the J there were different versions. The dinosaur vinyl used on the '51 cars was definitely darker and more "marbled" (more complex pattern/texture) than that which was used on the '53s that I've seen and owned.