I think so. Was it warmed up good? The 305 is gonna have to be in tip-top condition and tune before making any valid assumptions about emissions. Not just that but 1/3rd of emissions are evaporative. Lets all just be glad they aren't looking real hard at those systems! IMO, a run-of-the-mill monolithic cat with sufficient size as used in later model vehicles with similar displacement should out-cat the old pellet style OE unit, if thats what it had. If you get a cat advertised as high flow, well its anybody's guess if the results will appease local authorities. But a stock 00-10 truck cat ought to do, I'm thinking. Something like that. If your truck has a feedback carb (wires going to it), and its a Quadrajet, theres a less-known tweak called APT adjustment. Adjustable part throttle. Alters tension on the primary rods. Oop, paragraph getting long must stop! I can speak Q-Jet, if you need some of that lol.