^ agreed. Its a HUGE concern with glass, so I would worry more with a soft material like plywood that will inevitably flex...
I could understand if it was going behind a wall and the front want resing on 2x4's, but it doesnt seem you are going in that direction, and there is no explaination for the sides to overhang. The corners are the more important part (structurally) of every fish tank. Big or small. Wood or glass. There are no factors.