Update! Success! Or close enough to it. With the top siliconed on it holds enough pressure to overcome the head of the overflow system. The two 1" overflow/drains are enough to prevent a siphon from forming. The Rio 1100 provides enough power to cause a mild current through the tank.
At this stage, the only minor setback is developing a way to "burp" the display tank to purge the air from the area above the vent opening. This may be as simple as shimming the table to ensure that the overflows are at the relative highpoint and inserting a tube through an overflow to vent the area around the overflow then removing the tube, or as complex as drilling a small hole in the opposite corner of the overflows to fit an airline valve in order to vent the system, closing it after all the air has exited. Sea trials will determine.
If an airline valve is fitted, I can see this project slowly becoming more "fish tank" and less "
coffee table"...but at this point my only goal is stable operation.
-Matt