I'm having trouble picturing what you are doing with the 2 x 4's. If you are putting uprights in each corner, and then a 2 x 4 across the front (this would need to be a double header), then yes, your tank will be supported. My 40br, has no center brace, just 2x4's at the corners with double 2x4's across the front, firmly screwed into the "legs" at each corner.