Eshopps Eclipse Overflow Box Kit Large by Eshopps Amazon.com : Eshopps Eclipse Overflow Box Kit Large by Eshopps : Pet Supplies
I actually have the medium version of that on a 40b right now, it works quite well. Nice to see they're including the bit now.
The only concern I had was that the inside surface skimmer piece sits low in the tank (40b) so that the waterline is clearly visible 1" or so below the tank rim. I don't like seeing the water line, so when I mounted it i had to cut away some of the black top edge trimming on the tank so the inside piece would sit higher. If you go this option and want to know what I'm babbling about I can send some pics.
This may not matter to you but it does to me. So I am passing on one small piece of information for you to consider. Many of the less expensive overflows do not come with a cover for the box. I personally would not get one without a nice snug lid. IMO. The one nemesis of the over flow is snails. And covering the inside portion of the overflow will close to guarantee you will keep them out. Along with jumping fish and a number of other things you would like to keep out. Of course you could cobble some sort of lid but seems the cost difference just isn't that much. For instance marine depot has lids front and back is drilled been animal has a template and drill bit and is only 110 bucks. I have never used it and am not recommending one brand over another. Just felt you should be aware of your options.