New 180 Overflow Recommendations

I'm upgrading my 75 to a 180. The 180 is an old school glass tank with 2 corner drilled bottom holes. A 1.5" in the left back corner and a 2" in the back right corner. I'm having someone fabricate two black glass overflow boxes.

Question: I'm being told that setting this up with the 1.5" coming from the sump to the tank and 2" being the drain to the sump would not work.......Do I need additional hole drills for sufficient drainage?

Or, use both of those holes as drains and bring the pump input over the back?

I really don't wanna have to move the tank to get the holes drilled....since it weighs a ton!