No, sorry, I didn't take any pictures of the back before setup.....the overflow is right in the middle of the tank.....it has 3 trays right under the overflow but I don't have anything on them.....after the water fills up the middle area, it drips water thru the drip plate into 3 separate sections on each side, then goes all the way to the sides and thru the overflows.....I have bio-balls in these 3 sections. I also have 2 Fluval 404's right after the middle section that I run carbon in.....my sump is an Oceanic Model 3....I have bioballs in the sump also, where the overflows pour into. I'm using a Tunze skimmer right now and I may supplement with another skimmer....return pump is a Quiet One 4000.
The tank is 8' long, 24" high, and yes you're correct, about 20" + 4" on the back wall.
I considered that same Deltec model that you are looking at.....looks like a great skimmer, but I couldn't figure how to mount it, especially considering the canopy. The only place where the water is at a constant level and high enough for the Deltec input to reach is around the middle area.......and the canopy would get in the way.......you can't submerge it in the back area because it won't fit.....I'm sure you could modify something, I just felt it was easier to drill it myself, for the reasons I mentioned before.