uggghhhhh, glass overflow, my lfs had one just like it, cracks easily, now that corner of the store is empty, I prefer and recommend acrylic for overflow towers and wet drys.
I agree that glass isn't my favorite for over flows. I like the glass tanks with the acrylic overflows. I wouldn't trust the overflows not to leak so I allways use the tube to set the water level
I use pre filter overflows on some of the glass tanks and keeps baby fish out of the filters, you could also get the filters and use them if you use 1 inch tubes.
The drawing is very good, only one remark though.... the second hole in each overflow to plumb the returns up in the tank without having them come over the back. Sorry just being picky.
one hole is the drain the other hole is the return it should be 1 inch and 3/4 inch you could chose to use all the holes as drains but if doing fresh water on it i dont think it would be needed it lookes like a knock off of a starfire tank i think it was a canada made tank in which case they dont puts slots int the top it is just a flow over system i would go for the biggest sump under the tank that you could fit it will just ad that much more volume to your turn over
