The shadow effect only happens if you put a MH
directly over the brace. Its not overly prevlent with Florecent lights and if you balance two MH
bulbs on either side of teh brace the shadows cancel eachother out.
If the tank had a center brace then the center brace is crutial to the tanks stablility. The goodwill folks shouldnthave to much problem if you ask them to take the tank around back and fill it with water so you can check for leaks. At that time you can also check to see how bad the front and back glass bow out from the water pressure.
If its an allglass tank you can contact allglass about a replacment top frame. Its not hard to cut the sylicon off the frame and remove the old frame. THen use ample sylicon to secure the new frame to the top of the tank. I have done this with a 45 gal
tank that I got.