1967 Cadillac Deville 67 Caddy Exhaust system

As far as unleaded goes, you would need to call around to see what a machine shop would charge to install hardened valve seats in the cylinder heads. You could install a cat converter or two (one for each side) they will run around $200 a piece for universal ones. Also be sure there are no leaks and the tail pipe is all the way at the rear of thevehicle where GM put it originally. You may also want to find a shop that specializes in carbs, they may be able to fine tune it a little better so that it isnt so rich and stinky. Ifit s off, it will ruin the cats and possibly make them smell as well