I've got 13 in a 2x3x6. I'm sure they wont all be females so they'll be some thinnin around here soon enough. You could bend the tops over and grow them outward, then turn back to the center. I used to grow under a workbench no higher than that and utilised the sea of green method of pruning and bending. Workes good, no big tops but LOTS of smaller ones!
Good luck bro!