You didn't mention what year of car you have. The 1967 and early 68 Firebirds have an 8 bolt water pump and a 2 piece divider plate. So don't be to hasty about chucking your divider plates. If it fits in there it's probably the correct one. They also don't use the rubber donuts that come in the typical water pump gasket kit (those are for the late 68's and 69 Firebirds with the 11 bolt pumps). I agree that you need to be running a t-stat. Without one you don't give the coolant time to cool in the radiator before it goes through the engine. I would find one in the 180°-190° range.