I have a 75 DT and. 30 long sump.
I removed the center support while the tank was full and running.
I glued and screwed some 3/4 ply inside the top frame to add rigidity to the stand. Before I did this I removed the short perpendicular brace so I could get the widest thickest ply in there. I used gorilla glue and sheet rock screws.
When I took the center piece out I slowly cut it as low as I could with a hand saw.