Would the dimensions that UPD gives on there web site for the 1959 Fireflite come close to what you need ?
Glastron 1959 15ft Fireflite = 60 L x 17 W x 16 1/2 H
It looks from brochures and measurements to be the same boat(1958 & 1959), but no detailed pictures of deck shape.
You could do a Google search for "Aluminum extrusions" and find something to make the frame out of.
Hard to see in your picture, but do you have corner pieces ? The bottom ends, little triangles.
You could also try to make your own, with some plexy.
http://forum.cgoamn.com/index.php?topic=2901.0You can find the white bottom gasket on eBay or other boat supply shops.
1958 pictures ...