The original grand sports were made from regular 1963 Corvette Coupe bodies. The convertibles came about when they hacked the roofs off of two of coupes later on. Zora Duntov had molds made for the flares and modified the other components. I've noticed that Superformance did not hold true to the original design-no holes in rear taillamp panel, which uses standard 63-67 taillights, the parking lamps are not recesses, no slits in the rear quarters,etc
It would depend on the price, but i think if i were tog to build one currently i would go with mongoose. You can use c5-c6 suspension on their models, which is a huge plus to me. I do not want a transverse rear spring or small u-joint half axles in a sports car with over 400-500hp to the wheels.
http://www.mongoosems.com/GrandSportPhotoGallery.php