A buddy of mine has a '70 LS6 Chevelle, that is an original car, but is not a numbers matching car. He had put a set of repro chambered pipes on the car, because he liked the sound. Another friend has the same car, but with 2 chamber Flowmasters, and his car was 3 tenths faster. I would go with a nice set of Flowmasters with and a cross over pipe if I was looking at 1/4 times. IMHO.