The front inner fenders, footboxes and the frame looks very CCX as does the reservoir and the windshield center clip. Their is no gusset plate between the main frame rails and the kick up frame rails over the rear. The torsion bar frame mounts also look different. The trunk is unlike anything I've seen. That could very well all be prototype stuff.
I didn't know of them making a slabside but I will ask Peter when we talk next. They made 1 prototype
289 Shelby Cobra Replica - Featured Vehicles - Kit Car Magazine
and 6 of the FIA cars. I see that yours and the FIA's don't have the front side marker bumps and a pretty similar nose look.