You seem pretty new to RC, or at least the custom side of it. The center diff should come off with four screws form the bottom of the chassis. I really don't think that the RCM kit is hard to put together.

I would read, read, and read again the MANUAL FOR THE CRT.5 to familiarize yourself with the way it is put together. Just take your time and lay everything out neatly in the order you took it apart, so that it is easy to put back together.

Hope this helps!