Well, sorry to say that the experiment was a failure...
The spray bar only provided modest cooling, and--for practical use--would require a resevoir the size of the gas tank! This really surprised me, considering how much better water is than air at quenching metal, for instance.
Oh, well...can always find a use for the pump, and it won't be too much work putting the shroud back on. I think my next move is to close off from the front bumper to the rad bottom, to get the air to go through, rather than around.
Just wanted to report the bad news, in case anyone else was considering travelling the same road...don't bother.