With that kind of track experience you can just get your TT license, considering they usually lump-in HPDE4 cars in with TT, you're good to go. I don't know where the Mazda would run, you can look it up on the NASA site.

You're concept is valid and should in theory work providing you can figure out the ECU issues. This is the only thing holding me back from doing the same thing. It seems after two years of searching, nobody has the expertise to modify our ECU's. The only thing that I have found would be a custom piggy back MOTEC system which would run about $4,000.