[JesseK]

It would be more taxing on the team, but based on what I've heard I would recommend tapping the ends of the live axles and putting a bolt in them rather than using a c-clip.

Also, to prevent racking you could make this out of 3" box extrusion and make it a little longer at the bottom. That way you could have at least 1/4" wide strips running between the sides at the bottom. The aluminum already turns in at the bottom, so making it longer and cutting a hole (rather than a whole slot) for the wheel would easily allow you to do this.