Welcome to the site! I'm pretty sure that your car was a custom convertible, that was sent out to be converted into a vert. Convertedvertible. Another great site to sign up on and check this would be here. Four Eyed Forums - Powered by vBulletin
These guys really know their stuff about early foxes and would also be able to help you immensely.
Don't give up here though, as there are a few members that know their stuff about them as well.