Trim chickens of excess fat, rinse inside and out, and pat dry.
In a small bowl, combine paprika, chili powder, oregano, salt, black and
cayenne peppers, garlic powder and brown sugar; mix well. Rub about a teaspoon
of the mixture on the inside of each chicken. Rub remaining mixture over the
surface of the chickens.
Open beers and pour off (or drink) about half of each beer. Stuff the diced
onion and garlic into the cans. Ease the chickens over the beer cans so that
they remain upright.
Place chickens and beer cans on grill. Close lid, leaving vents open. Grill
for about 2 hours (if you use a gas grill use lowest setting), or until legs
and wings wiggle easily.