If you only uses the standard rear Brake, then you can only use a single servo for throttle/brake.

You might only need to 2 brake servos if you plan on mounting front brakes. There is no need for that with the standard rear brake.

But if you are afraid that you won't have enough braking power, then use the new Hitec HS-5955TG at 333oz or 24kg/cm.

btw. the HS-645MG at 133oz or 9.6kg/cm does a more than adequate job in my Leopard Race.

Here is a pic of my frontend with alu from 3 different makers, and a dual steering servo setup.