That shouldn't be your problem though, right?
Interestingly, STU is the only ST class where the index dropped, and it dropped a lot (.827 to .81. I think an STU RX-8 would be an interesting project - excellent suspension geometry let down by overly soft stock springs (which can be cured in STU), and it has room to run 275/285 tires on 9"+ wheels at all four corners, while the rally cars are rules limited to 245 max width. It also weighs 200-300 pounds less than the rally cars.