Oh wow....I would not keep a shark in a 8' x 2' tank, no matter how tall it was. they need a large footprint to roam. Take them to the public aquarium or possibly trade them for credit at the LFS
You are right, it will be extremely hard to light a 6' deep tank for corals, but, depending on the way it's constructed, you may be able to build some sort of submersible background that you could attach corals to around half way up. You can light a 3' deep tank with minimal effort.
You could do tangs, angels, triggers, eels, look down fish..there are many.