It looks like a standard internal overflow. Those pumps with the filter media looks like maybe they went into the overflow box and circulated back into the tank. The overflow probably still functioned and they had a sump. If the the bottom of the tank is drilled with one or more holes, chances are good they were using a sump with a normal return and those other contraptions were for filtered circulation only.
Then again, looking at the photos closer, it could be some sort of internal filter...maybe? The weir is saying its an internal overflow but the separated areas say something different. Could be home-made-DIY-ingenuinity.
Good Luck.
Look under the tank for holes.
Just got this 130 gallon off craigslist the other day for $300 with the stand. Very happy with the tank other than the load of scratches inside the glass going to see if cerium oxide can take them out anyways... This tank came with an internal filter i think this is maybe its an over flow box which im hoping it is because i wanted to run a wet/dry refugium underneath without need for a HOB overflow... But i cannot figure out how to set this thing up ive never seen anything like it.... If you can look at the pictures and give me some ideas it would be appreciated... I found what i thought were possible manuals online but couldnt understand them not sure if they were for this model. 
