The internals are all the same for the most part, the one difference being I opted to upgrade from the Gold to Silver Spark motors from Fingertech. The big difference now is the 3D printed body. The overall dimensions are roughly the same, but the body is now one solid piece. The motor mounts are designed specifically for the Silver Spark motors to slide in. Each motor is prevented from rotating due to the oblong shape and is clamped in by a lid that is kept in place by two screws. There is also a mount for the servo to slide into. That will be kept in place by servo tape and the 3D printed lid (not pictured) secured by 4 screws.
I've been working on tweaking this design lately. The problem with the design pictured is weight. As shown, the bot would only weigh around 14 oz. Currently I'm working on beefing up all of the walls to make up for this, but feel free to comment on any ideas that you have on what to do with the extra weight.