150 watt hps would get to hot inside any closed box that small. i suggest cfl's at least (1) 100 watt for any yield at all. It will be a small yield though. its really not worth it. get a real space to grow in
It might be hard to start this late into the plants growth especially if the stocks are to thick and woody already, but you might have a chance if your strain stretches alot during the switch. always water before training to help bend the stems.