Your drawings seem a little confusing to me if you could label them or explain a little better what your looking to do? or an actual picture would be great. I was guessing that the tank is in a wall that you can see on both sides but how are the magnums located is the wall hollow on both sides? In your second sketch; are there doors above and then two below? second question how big are the magnums that you are looking to replace with a sump? I personally have a thirty gallon sump under my 150 and wish i could go with at least a fifty gallon.