I think a TT02 Spec class is a fantastic idea. I personally would allow for any Tamiya TT02 hop up. (TCS style) Reason being, none of them are a huge game changer. Eventually overtime all cars would end up catching up with same hop ups. Eg if the fast drivers are running the Type S arms, eventually the rest will catch up.

I would however disallow non Tamiya hops ups, just to keep things more aligned. Again none of them would give a huge advantage, with the exception of the Yeah racing motor mount, which gives greater gear options.