Congrats on the free tank! But, personally I wouldn't consider it a very good candidate for a stand. It appears to be constructed from 3/4" MDF with minimal frame reinforcing.
When you recall that the water alone is going to weigh 625lbs (8.34lbs per USgal)....plus aquarium, plus substrate, plus decorations, plus equipment...your set-up will likely exceed 700lbs., and I wouldn't trust that construction for that load.
If you're prepared to do some major reinforcing you could make it work, but it would likely be easier to build a new stand from scratch, and then you could select materials that are better suited (MDF expands and becomes brittle if it gets wet).