I really believe that you're going to have to get as many stills from the movie as you can find, and analyze them and blow them up and try to figure out what you might like.
Brando has had his picture taken in publicity stills for the movie on half-a-dozen different bikes from Triumphs to Matchlesses to Moto Guzzis, since, to the non-motorcycle riding public, a motorcycle is a motorcycle and they can't tell a Harley Davidson from a Bantam. And if that movie is like most of them, he probably used 3 or 4 different bikes even filming the movie.
Remember the movie "Babe", about the pig who learned how to herd sheep? They used 48 different pigs during that movie, all just about identical, starring as "Babe".
Me, I want one of those blue-and-yellow sweaters like Chino had, and a Hydra-Glide just like his.
Good luck! Should be fun getting Johnny Strabler's bike, the way it's imaged in YOUR mind, together!