I've got a 69 Buick 350 with a very damaged driver side exhaust manifold. I've found a manifold off a 72 Skylark on eBay, but on it's list of vehicles it works with 1971 is the oldest model of any model. Did the heads change between 69 and 71? Also this is a fsj 69 J3000 camper special, if that matters. Thanks!