So as I read it you are going to run a nitrous plate beneath the carb and by latent heat of vapourisation it cools the entire intake charge. That will work, the further up the intake tract you place the plate the better the effect will be. I mean it will condense the charge of air, fuel, NOS mix by increasing its density.

There is only one drawback though, NOS mixed wth fuel is an explosive mixture and under compression in the blower manifold, under combustion in the cylinder where it is supposed to happen that is fine and gives you the jump in torque that you require. IF YOU GET A BACKFIRE INTO TH BLOWER MANIFOLD with the roots blower pushing a fuel/NOS mix you are going to get an allmighty BANG. You had better have a good pop of valve. I would go so far as to say get some good quality blower bolts and hold down straps and even install a blow out panel. Or else you might see your blower if it is mounted on top of the engine go into orbit !!!