yeah, those "bump extentions" are to pick up the box. They have a locking mechanism on the inside which correlates to the bolts on the box. Though they could have engines attached if thats the best design concept.
(Your recoloring and design tips have forced me to think with a lot more of a logical critique on how it would move as well).
The reason that they were positioned on the arms was for stability during flight. if the ship is ballanced on those two columns of thrust, it'd fall forwards or back. but if they were positioned on each leg. Four colums of thust are much easier to ballance on.
What would be your suggestions on that?
(Oh FYI. In the last example of mine, I only placed the engine on the forearm, in the final one id have the engines on all four... so it would look balanced).