I think they should. The basic chassis parts are the same as the RS4 2. The only difference in the SS is the addition of the SS engine, the 2-speed, and the turnbuckles. So they should fit the RTR just fine.
If what would work? The header? I wouldn't use that header anyway, everyone who has it says it is VERY thin and warps and bends easily, however check out this duratrax header, I just ordered two of them, one for my RS4 3 and one to try on my Maxx. Check out the price too! But both HPI and Traxxas headers are the same size and are interchangable.
Cool. I'm close to updating my Maxx exhaust. And I'm not sure which to get. Hey! Then I can put the Traxxas header on my RS4 3! Sure, it's not ideal, but it's better than that cast nightmare that comes stock!!!