Yes hillage, that is how my overflow is going to be. The one on the inside is the one with teeth, and the one without will be on the outside. All of the pictures are in the original first post.
I have found some clamps that I am going to use.
I connected my sump containers. Had to do it in a U shape because of size restraints. It's still going to be really close to not fitting in my stand. That would suck.
I have the water coming in through filter media, then filling up box 1 and exiting to the right, then filling box 2 and exiting to the right (this was cut lower so the water would flow down), and then into box 3 and up through the pump.
Right now I just have them silicone'd together. Tomorrow I'm going to run another bead of silicone along the edges and then clamp them together.