Yes the SS does indeed include the .25 engine. The pipe for the ss is an aluminum rippled tuned pipe, very similar to the paris ripple tuned pipes for .15 mills. The 25 rtr comes with the same composite pipe as the .21, I don't like composite pipes personally. As far as the three shoe clutch, I have no idea why the did not include one with the SS kit, I have since purchased one and am getting ready to install it. The fuel tank on the SS is still the old style with the primer, I personally do not like tanks with primers so I have replaced that on my SS as well. I just saved the original in my box as an emergency back up tank. I enjoyed building it, much more than I would have just buying the rtr. Not to mention by assembling it yourself you familiarize yourself with the vehicle, and when a problem arrises you know how it went together so it makes working on it much easier. I also like the clear body, I don't want the exact same paint job thousands of other guys already have. So I guess I am biased towards the SS, yes, get the SS, LOL.