Actually it's pre 49 and it's HOT RODS not street rods. In 1949 Ford, General motors and Chrysler all changed to wider body styles that had rear quarter panels instead of removable fenders. Studebakers were a few years ahead of the big three on this design. Hot rodders didn't like this new style so they kept useing the older body styles from 48 back. It's kind of outdated now that there are so many nice 50s and 60s cars but it's still fun to go to a show where everything is pre 49.
So a hot rodded 55 Ford ranch wagon could be a street rod but not a hot rod by the original definition.
A friend has a Kenworth that he rebuilt himself. He calls it a hot rod. Why not. If there's hot rod boats and bikes then it's a KW hot rod. It's an ever changing definition.