I am helping a real newbie out here in my patrol area who bought and daily drives a 72 Tbird with the 429. He is leaking coolant behind the timing chain cover and his water pump sounds like he is sawing rocks. Anyway, we go to order a gasket set and it says "with or without sleeve". Why would a certain engine from a certain year have two different type of gasket sets? Why would the harmonic balancer sleeve be or not be there with the same engine. Is this just auto zone suckin'?