Stepps, I have an HPI RS4 3 RTR, I added the two speed tranny to mine, as well as an OS 10e carb, and better header. It is not very difficult and it will come with everything you need. However can I suggest going with the SS? It already has a two speed tranny which will cost you another $55, two needle carb, figure another $50-60, where as the RTR has a single needle car, and you WILL want to change that stock carb, it runs crappy with that carb. The RTR also has a terrible, restrictive exhaust header, the SS has a much better header, and the SS engine is considerably better than the 15 FE in the RTR. The SS also has adjustable turnbuckles where the RTR does not. Out of the box the SS is a much better car than the RTR. You will need to buy a radio, reciever, and two servos though for the SS. I am not sure what your budget is but the SS runs about $269, then you can get a great radio like the JRXS3 for about $200 more which comes with two servos and a reciever. So for about $500 by the time you buy a glow igniter and some fuel (which you will need anyway for the RTR, you will have a very nice car and radio. You will easily exceed that adding all the aftermarket parts just to get the RTR where the SS is, and you will only have an OK radio and servos as opposed to a really nice radio and good servos.