This is the only known picture of a 1958 retractable prototype. Thanks to Jed Zimmerman for the photo. The photo is supposedly from the Ford Motor Company archives. Many books and magazines have mentioned this "clamshell" retractable, but his is the first photograph that I have seen.
The photo leaves a lot to be desired. The break in the hardtop could have be drawn in. It is not even possible to tell if this is a 1958 or 1959 Thunderbird. Proof of the existence would be more convincing if there was a picture of the top in a partially retracted position.
Are you convinced that that there was such a 'Bird? If you have any more pictures of this elusive T-Bird retractable, contact me at Alexander.