A few companies were producing aerodynamic fibreglass hardtops for the MGB Roadster in the mid 60’s. I guess after the MGB GT came out these folks thought that many roadster owners would be interested in a similar fastback style car. The lower Sebring GT certainly has interesting lines with the spoiler type tail. I’m not sure about the J&S GTB conversion however.
These aftermarket cars certainly seem to be based on the 1963 MGB Coune Berlinette which predated the MGB GT by 2 years.
Has anyone ever seen one of these? They do show up on Ebay occasionally but all the ads that I could locate had ended. Would sure like to see one in real life.