I used to own a 74 Duster with a stock 318 that I put el cheapo headers on. I eventually destroyed the headers on a road trip and had to saw them off with a hacksaw. I replaced them with a set of 340 A body manifolds from a 72 Duster 340 and noticed absolutely ZERO difference in performance. Find you some 340/360 A body manifolds and send it! The drivers side A body 340/360 manifold is the exact same thing as a 68-71 340 HP manifold, with the exception of having a boss cast into it to hold the heat stove for the tube going to the air cleaner. Passenger side is same for A-B-E bodies.