Curious, why two 660 ballasts? A 660 can drive 4 X 48" bulbs on its own..
Also, I would seriously consider getting those ballasts out of the stand and onto the back of the canopy. There are few reasons. That area is just bad in general for any electronics, with a much greater chance of corrosion, or worse, direct salt creep/splash. Also, in the case of an overflow, a fire hazard. Another reason is if you need to remove the canopy to work on it, it requires much more effort in that configuration, as opposed to just unplugging them and removing the whole canopy by itself. There is also better cooling outside the stand. I personally removed every bit of electronics out of the stand so if it were to overflow, I drastically reduce the chance of major shorts/damage.
Here is how I have mine:
Nice start though! That will definately be a SPS tank. You will find that amount of light will burn many LPS and softies..
Grow out some SPS and create your own shade for them though.. heh