All of what you have described is just typical bolt-on parts that could have been added by anyone, and not necessarily a dealer. Not sure what a "California gauge pkg" is, but I have never seen it done by any of the west coast supercar dealers, or any for that matter. That looks more like a home-built job as dealers were not into making custom panels as they wanted to make money quickly, and not have the car sit around waiting for true "custom" work to be done. They would install the aftermarket underdash gauges from Sun, SW, Autometer, RAC, etc. using the gauge manufacturers panels to install them: 2 or 3 screws and you were done. There is only one dealer supercar that I know of that had anykind of custom gauge work and it is a 68 Motion Camaro which had the factory speedo & fuel guage replaced with a Stewart Warner speedo & tach. It was a simple swap done in probably a few hours, nothing like the panel shown in your pictures that required some serious fabrication for proper fitment. I have never heard of any reinforcing plate welded to the driver's side frame-rail for structural reasons, can you post a picture of this item? Also how about some pictures of the other items you are describing: the rev limiter, welded areas on the spring perches, the slapper bars, and maybe some overall pictures of the car. The more information you can provide the better chance that someone will be able to help you identify your car.
If you feel that Dick Harrell had a part in the car also, then you need to contact Valerie Harrell as she has a lot of new found paperwork from her dad's business, and there were two cars that were once undocumented that she found their original paperwork in the boxes. I will send you a private message with her email address .............RatPack......................