Making 60 vast or 120 certainly ample, servings

Multiply all quantities by 30, so:

30 medium fryers of about 3 lb apiece, quartered
3¾ cups olive oil
15 lbs onions
90 cloves garlic, chopped
3¾ cups tomato paste
480 fl oz tomato purée (3¾ gallons)
½ cup basil
½ cup oregano
30 bay leaves
2 Tablespoons celery salt
5½ lbs mushrooms, sliced

Special Instructions

When you're cooking this much chicken, it's much easier to bake it in the oven rather than splatter up your range. In which case you'll need some roasting pans. About an hour in a preheated 350° is good; maybe an hour and a half if your trays are densely packed.