What I'm thinking regarding the plumbing is to eliminate that huge check valve. That thing belongs on a submarine or an oil derrick out here in Texas.
![Wink ;) ;)](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f609.png)
'Resistant' isn't quite a good a guarantee as I would want. I'd probably pull it apart to see what all is inside, and if I didn't like what I saw, it would be returned.
What I would probably do in your case is get a few more bulkheads (or Uniseals) that match the ones in the base of the tank (same diameter). Get some PVC pipe that fits the bulkheads (and/or UniSeals) and spray paint them black with Krylon Fusion. Insert those through your new overflow box and down into the bulkheads at the base of the tank.
In that way you have your drains going straight down, and you have returns that are plumbed up and out of the overflow where you can drill a few siphon breaks.
You would see four rising pipes unfortunately, but black will help make them less visible, especially if you decide to put a black backing on your tank one day. Clear acrylic tubing would work as well, but it would grow coralline in no time and become ugly internally, similar to seeing someone's overflow area through the back wall of the tank. White would be ugly. If you really hate seeing the pipe, you could affix two pieces of black acrylic in front of the two sets of pipes, securing them in some manner. That would keep the PVC out of sight.
Another option, which is really out there, is to reduce it to two drains only and seal the other bulkheads off. Then have your returns rise up behind the tank directly behind the drain pipes, which would kind of hide them when looking at the tank head on. The returns would come up over the back of the tank and into the water, with anti-siphon holes drilled of course.