So the biggest problem is 2 fold.
1. That's not a grow light exactly, so hopefully that glass cover is not too thick or coated with anything that would take away from the effectiveness of the bulb. Sealed grow lights use glass that will allow for the most amount of spectrum and light pass through without loss, but, there is still loss as apposed to open reflectors.
The second problem is that usually one of the reason people try to keep ballasts out of the room or as high up in the room as possible, is because they create a lot of heat as well. It's not just heat from the bulb, that whole unit will emit a lot of heat because the ballast is attached to the socket unit.
As for mounting, I would take the unit apart, and see what your able to do. Judging by the coating of that light and the colour, it's old-school and the case is probably cast. It weighs a ton. I would drill through the case from the inside out of course and rig up 4 "eye" bolts, in each corner and run 2 lines to the ceiling.
Oh yes and I was just thinking, that shape and material of the unit might cause heat to be projected down at your plant, I guess it all depends on the path of least resistance for the heat to escape.
I would also try running it for a couple hours before you put it over your girls and do some heat checks, use your hands and measure how far away you can be and what kind of Temps it gives off. No need to fry your girls because the beast is just not meant for this application.
All in all, good luck. I use a 4' 4 bulb HO t5 to veg and it's doing awesome. I'll be tossing the 400w hps with a 24" batwing up in 2 weeks for the flowering cycle.
