I've just noticed the "solved" title of the puzzle - strictly speaking this car isn't a monoposto, it's one of the dual-purpose cars of 1949/50 which could be raced either in Formula 2 , or with cycle wings fitted in sports car races. Which is exactly why they were made that way, to maximise the chances of entry in as many races as possible. The HWM team were constantly strapped for cash, and relied on starting and prize money to survive. The new car for the 1951 season was a monoposto.