We spread broiler litter every year. I'm hear to tell you it will grow grass. You need to get it straight out of the house if you can, litter out of a stack house will grow grass bit not as well. That stacked up litter goes through a heat and just doesn't work as well as "fresh" crap.
We spread a load / acre with is about 1 ton I guess. You can't go wrong with it at all.
Do you know how big of chickens were in the house, 5,6 week birds or older. The older the birds the better the litter.
Also when was the last time the houses were cleaned out?