Found the stipulation in the rule book. I like to see it in black and white, our regional events are strict. This should definitively answer the question. Regional events yes, national events no.
Completely stock, you can run BS. Although from my experience, the Cup2s do not get up to temp quick enough. Went through two full sets out of 8 events. After LTH, tune and e85 had to run ESP. Switched to the BFG Rival S 1.5 so I could run CAM-C, much cheaper $312 each and honestly the car felt...