Suggestions needed

Has anyone tried to retrofit a coast-to-coast overflow into an existing tank? My 180's (both) have semi-circle overflows in the back two corners. I want a coast-to-coast over flow in each tank. If the overflow boxes were square it would be fairly simple to attach to it and build the CTC. With them being semi-circular its a little more difficult. Another option is to remove the semi-circular and replace them with the square corners then build the CTC with those. The main issue is that both tanks have a center divider in them that prevents me from simply inserting a solid sheet of acrylic in the back of the tank. The tanks are 24" front to back. I would like to have a wall 20" from the front to give me 4" in the back for drains, returns, and pumps (for a CLS).
I have never removed the top of a tank and reinstalled it. That would be the simplest solution but don't know how. Anyone every done that?

Any ideas and/or suggestions are greatly appreciated.

 

I wouldn't pull the top brace on a tank that large and expect it to go back together well enough for piece of mind. Have you considered doing a shallow coast-to-coast overflow? I've installed several Bean Animals this way with only about 6" of height inside the overflow. This leaves more room below it for rock scaping and should also make it easy enough to drain the tank far enough to install while keeping the reef intact.

I also attached a sketch of a way that you should be able to tie into the existing overflows easily enough.

 

The shallow box was my first thought and may end up being what I do. The idea behind the coast to coast was to be able to hide 1 or 2 pumps behind the fake wall to hide pumps to be used for a CLS setup. I could do a partial shallow box for the overflow and then either put a fake wall below that or hide the pumps in the rock work. I tend to prefer cave type entrances and a black wall behind it would seem to give it more depth to me.
The partial wall beneath the coast-to-coast wouldn't have to be watertight, it would even work better if it weren't. If its not water tight then it will help with water movement through there to cool the pumps. I don't like the idea of putting them in the rocks because of maintenance issues. Trying to clean and/or replace a pump could be a total nightmare if its hidden by the rocks instead of a fake wall.

I wonder if I could remove the overflow boxes, make them 6" wider. Right now they are semi-circles in the corners. If I made them 6" wider then it would give me room to put the pumps in the overflow. Then do a shallow coast-to-coast at the top for drainage. I suppose I could just make them square if I am going to remove them and put them back in. The overflows in it now are the ones that have drainage slots at the bottom for bottom movement so extending it might work better to keep the bottom drains.

OK, enough rambling for now. Any thoughts and/or ideas?