Never heard of it, after looking up apparently is rare. Don't know why he painted it that color. https://orlando.craigslist.org/mcy/d/1962-mustang-pony-with-title/6974091735.html
Cute little Flathead. Would make a pretty neat pit or parade bike but, street legal or not, wouldn't want to be on the road with traffic on that.
Met a guy who had a collection of them here in Hawaii. He also worked on Cushman scooters. Rebuilt Briggs and Straton motors for them by lengthening the cranks. My uncle made molds for making the bodywork for them. Cool collection, wonder what happened to it all.