How are you running clean solution through it? Is the keg going to be upside down?
I clean kegs with a sump pump in a 7 gallon bucket with @ 2 gallons of PBW solution in it. I spray the inside with a crude version of your spray ball, it's a 1/2" PVC pipe with a cap on it. There are holes drilled into the pipe at the cap and along the sides. The keg is placed upside down in the bucket and the pump is turned on. The only thing I really can't clean well is the dip tube. I wash for @ 20-30 minutes depending on how bad it's soiled. It works really good for Sanke kegs.
The spray ball is definitely nicer then my PVC pipe, I'll bet it will cleaner faster and better than just a pipe with holes in it.