You just talking about the Castle creations speed control and motor? I was unaware they made a conversion kit. If they do, hopefully someone will chime in.
The MMM is a good speed control and in my opinion the 2650kv motor is a bit much as is the 2000kv truggy motor. They do have motors in the 1800kv range that would be better in my opinion, but I don't know if you can buy those in combo with the ESC.
Losi's 8ight electric conversion works great and is cheap.