Siliconing boxes in place;
Acrylic you'll need to have made as I doubt you'll find something attractive out of a box. Won't be leak-proof. Think about ALL that tank water making it's way to your sump during a prolonged power outage.
Glass is much safer but won't be pretty or easy to disguise. You can get smoked glass. Figuring out how to incorporate a weir or have glass machined with teeth can be a challenge/costly.
Replace the current bulkheads with new (or new gaskets) and plug them.
Drill the back or an end for a ghost overflow.
Use standpipes as previously mentioned;
Still recommend new bulkheads (or new gaskets).
Not the most efficient for surface skimming but will get you going.
Some PVC cut to the desired running height and returns plumbed in.
I saw a dentist's office with this setup and it wasn't TOO ugly with all the hardware in the stand. Viewable from all 4 sides.
Find another tank to buy
