Well that space is a similar size to the homebox xl, whcih is 4x4x6, and is IDEAL for a 600watter!
You will be happy putting 16 plants in a 4x4 flood/drain tray, or 16 1-gallon pots, and flowering at ~10 inches or so in a nice sea of green setup. Dusto2k3 is running one of those things and you should DEFINITELY have a look at his log! mmmmmmmmm coco.....