The 304 needs a different intake manifold to accommodate a 4-bbl carb. I researched this issue a number of years ago and found that the 4-bbl needs a high rise manifold from one of the other AMC vehicles so equipped which included some Pacers, Matadors or Ambassadors.

However, check Edelbrock as they were supposed to be marketing a manifold that would fit.

The fender well headers may involve some articulation restrictions. personally, I am partial to the closer fit with a crossover pipe and a single exhaust.

John Stewart
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