I think all Pontiacs through 1974 had dual exhaust crossmembers. It wasn't until 1975 and the advent of Cat convertors that the crossmembers had only a single hump. Also, both 455 engines had the 067 cam shaft, as per the Service Manual, the AMA Specifications and my 70 Bonneville 455 360 that I have owned for 41 years.
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