sleepydoc
Team RC
there is a pair of plywood pieces on either side of the corner going from under the top frame to the bottom frame. The cherry face frame isn't load bearing from what I can tell.
I think you will be fine. The corner support will ensure that the plywood does its job properly. Being a 75g and having 8 vertical pieces really spreads the load around.
The other mitigating factor is that there will be a sheet of plywood on the top that will distribute the load and potentially transfer it in to the triangular posts. That said, it would be better to have the load directly over the solid posts, rather than over the plywood frame. Unless the vertical pieces are totally snugged in, you are potentially depending on shear forces to support the tank, as Uncle said.
There don't appear to be gaps between the vertical plywood corner pieces and the horizontal frame pieces, and the top of the frame appears to be totally flush with the pillars, so with the 3/4" plywood top it will probably be OK, but it definitely gives one cause to pause...