Thanks for the replies guys. You've given me a few things to think on...
24" on-center might be stretching it a bit for the top frame..
I had also considered supporting the top braces with vertical 2x4s, and may.. It would also provide a nail strip for putting together the front vertical supports (though, the weight is still supported by screws in that case..).
I want to keep the stand 24" at a maximum because I will be viewing this tank from a severely reclined position on my couch for the most part

Also, it makes working in the tank a LOT easier (no step ladders here!). And, given the depth of the tank (36"), I also wanted to be able to have a good top-down view of the tank. It will be run as an open-top display..
Also, no equipment whatsoever in the stand. I run a basement sump.. I will need to get underneath to the back of the stand for any potential plumbing mis-haps though..
So, back to the [SketchUp]-board.. I'll be back in a day or two with some more designs for you to critique
Also, I'm undecided exactly on how I'll be skinning/finishing the outside of the stand and what sort of shelf/drawer options I want. My focus at this point was getting a stand together that will support the weight, and then see how much room I had for the other stuff..