I'm with Chief on this one; the requirement for catalytic convertors from model year 1975 onwards was a federal requirement. 75/76 107s had the cats integrated with the exhaust manifolds (as did W114s and W116s with the M110 engine). Non-catalytic thermal reactors were a 1974 California-only device. Outside California the 74 systems were the same as 73, i.e., Federal.