The body on the DC is taller, also the headlights and turn signals are very different on a double cab. I'm not sure if the bolt locations are close enough but I see the headlights and signal holes as your biggest problem.
Best bet is to call a company like Glassworks or McNeil, talk to the manufacture. I don't think anybody on the first gen forum here has fiberglass.
TundraTalk.net forum offers the most comprehensive collection of Toyota Tundra information. Find discussions on the Toyota Tundra Diesel, TRD Pro, SR5, lift kits, towing capacity, classifieds, and more!