Renjie- I mentioned the B4 site four posts up!!!
You can get the Mx-3 with one servo or two but I'm telling you they are $10 p[lastic gear servos that will strip in a day...buy upgraded servos!
T-bone just go to that site and do some searches...you're questions will be answered many times over...
Oh and I run a B4 and a T4 and have seperate electronics for each...switching them out between cars would be a MAJOR pain