I do not know about MBX4, but if you can compare diff. housing from MBX5 then you will get an answer.
As for brakes, with center diff, you need to use original disk brakes or combo. In my case, due to the fact that motor is too close to the diff, I am utilizing front disk barke and rear electric motor brake. Just electric wont do the job, unless you make your center diff. very tight.
Artur
P.S. I make this pinion from original mugen pinion