u could try and filp the center diff and motor mount 180 degree so that the motor will be in the opposite side of the servo , then ull have space at the back to pit 2 packs of lipo , although im not sure if itll work coz i dont have the stock chassis
I know RCM's ext. chassis would give me plenty of room, but I don't want to go to 1/10 scale or bigger (actually don't know the scale of RCM's chassis).
Flipping the diff and motor won't work, cause the motor wouldn't fit between the motor mount and the steering post.