Update: I put it into a floodlight that was originally for 100w MV cram Ed 17 minibulbs. The ballast and bulb fit perfectly so the optics aren't screwed up. 
Hey that's pretty cool. Did you have a pic of this constructed fixture? I'm currently building a custom Regent patio lantern with a 50 watt MV bulb and 35/39 watt MH magnetic ballast.