grow box

I'm not sure if grow box is tall enough i have 35 inches from light to medium
i have a ebb & flow and a 400 watt hps running 250 cfm for intake and out take light is inclosed and vented so the heat should not be a prob.
the only way i could get more room is
1. seperate ebb & flow and run side by side instead of on top of eachother
2.tear down closet shelf and redo box
so my question is is 35 inches enough room to grow a good size plant and produce a good yeild. I have gone this far and i want to do this right the first time (babies will be her in 2 days) so i need to get er done quick like.
thanks for reading post late
sdbud
grow room is now finished /i made my box 8' tall "watch out boyz cause here i come it's on like donky kong.!
babbies will be here in 2 days its a really strong clone of some "silver"

That's tight, dude. SCROG may be your best bet. I have a 250 hps, and I can get within 2" of the tops safely, but I think the 400 needs 6" or more.
What do you mean by 35"? Bulb to bottom? Or usable space.

thats the room from rock to the top of glass on the light.