Levelling it might be difficult, but otherwise that would work. I'd actually make a box frame out of the timbers just to hold them together, but thats just my oppinion. I made a stand for my 3' 65g out of just 2x4s, works great
That's what I'm trying to figure out, I've seen 3 foot tanks that are anywhere from 30 to 90 gallons, and these are the common sizes. For a 30 gallon with a 3'x1' footprint, cinder block on the 4 corners with 1" plywood should suffice, I would build a frame with 2x4's like you did for a 65, and for a 90 gallon with a 3'x 1.5' footprint I would support the corners, as well as the center using 6 piers of blocks total, along with the 2x4 frame.