By 1975, all passenger cars by Federal EPA standards, had to have a catalytic converter exhaust system. Since this standard was just being put in place, it's entirely possible that some early production vehicles got some type of special exception? super early production 1975 models? If you go on the EPA site, all of that early documentation is available to review. But I think it's safe to say, if you select a 1975 or newer model, you are going to need the proper converter kept on that vehicle by any state that is strictly following CARB standards set by CA.
