Can you cut out a panel, cut the panel down to 18" and reglue.
Then you'll have a 72x39x18. This will be much easier to aquascape, and would look stunning imo.
If not, you'll have to go tall and thin.
Go for whips and fans to accentuate the height. Don't try to pile up rock, it will require too big a foot print. Tall sarcs would look good too.
SPS would be tougher, but doable. Bear in mind that the SPS will tend to grow outward more than upward, to maximise their light exposure. They will then shadow whats below.
I once saw a tank similar to yours in a pet shop overseas. It was only 2/3 filled with water. On one side, the rockwork was piled up to the surface of the water. Inside the rockwork was a claear plastic shelf covered in sand/mud. A few magroves were planted, as well as a couple of other shoots. Mudskippers wallowed in it, and I thought it looked pretty cool. Quite different.