That line in the book is for re-inspection at the event after you already had the car inspected and want to change class.
So questions
Have you ever run this car yourself at Bonneville?
Do you have the log book to go with that frame sticker?
My opinion... you have a new car.. a roadster, your log book will show it used to be a coupe, but I would put it in the new car line... because it is a car change, not a body modification like going from production to altered by covering the headlights.
Oh, my opinion... well it is just that... how I would do it if I did it...
add.. Dan is on with some of the same questions... he types faster