From the reflector page.
"Q: Hi, What is the mogul socket number, will it fit a 600w, 1000w ? Thx
A: Standard mogul base. It will fit either of those lamps"
You DO NOT want a 600W bulb in a 12" X 12" area. If you missed that before ordering I would not recommend trying to DIY a fixture, the quickest and easiest way would be to just buy the Exo-terra hood for the terrarium and use there daylight bulb or any daylight compact under the recommended max Wattage.
Here is another link to a terrarium that is no longer being maintained properly using the standard exo-terra light fixture with one of there daylight bulbs. It is sitting on the floor and gets just enough attention to not kill off the few plants I have not moved yet. It is on my list of things to take down.