The “roadster” was an appearance package added by the dealer consisting of a fabric roof covering and Roadster lettering on the C pillars.
Yes, I got that, see my previous comment.
Really poor choice of name from the aftermarket people.
A roadster is a convertible, usually a two seater. Pre-war roadster often had rumble seats. The post 57 T-Bird “roadsters” utilized a fiberglass cover for the rear seat.