If you are comfortable working with acrylic, get some black or blue acrylic about 1/4-3/8" and to the left or right of the overflow make a box in the shape of a typical overflow in a RR tank; glue it in place and make sure it is watertight. it should be slightly higher than the height of the tank so that if your drain gets clogged, it doesn't overflow into the "dry" well. For example, make it 5x5x5 and then you can keep the dry side in the "dry" well and the wetside in the tank and then you won't have to spend more money on an insanely powerful pump.
I don't know if you like the idea but thinking out of the box works sometimes.
Best of luck on your build, it's looking good.