bongo its not uncommon to use hid lights in wooden cabs in fact, it is quite common with some common sense installing the light and good ventilation it doesn't pose any fire risk.
manowar have seen 400 hid used on scrog in 2 by 3 and 2 by 4 foot cabs with similiar heights with good results however you may want to pick up a 250 ballast and bulb as it is more adequete for your size with the 400 you are over 90 watts per sq ft with the 250 you are still at 58 watts per sq ft and it would save energy and be easier to cool. with the limited height you almost have to do a scrog as by the time you factor in the light and pots or hydro system you dont have much space left to grow a plant in a traditional way.