Gary,
Tony Branda has some of the best fiber glass I have ever worked with. Of note there are a couple versions of these extensions. One to fit a car without the installation of the GT/CS tailights. And one to fit with the tailight panel.
I have a set of the sheetmetal that covers the holes the cut in the stock tailight panel to fit the installation of the GT/CS taillight panel.
You should call them first and explain what you are doing. The Shelby convertible trunk lid will work, but it has holes for the Shelby letters.
Have you consdered putting the 1968 Shelby nose and hood on your car? I have considered it before! It looks great!! You could build a Shelby coupe clone and it would be a huge hit in the modified crowd.
Of course be ready for the some flak from the puriest people. Tim on our site has a beautiful GT/CS clone. He represents it for what it is and it is cool!!
http://www.cobranda.com/19shspendcap2.html
Go for it!! I built a 1967 GT/CS coupe clone so to speak. Did not use the script, just the stripes, side scoops and trunk lid. No tail lights. Put a 69 Mach I hood scoop on it and a front air dam. Loved the look!! It was a obvious clone, so no one gave me much trouble.
Welcome aboard!!!
Rob