The headers I used on my 350 to 455 conversion in my 76 are set for both. Either way it is never easy putting headers on either one. There is not that much difference in size (width) from Olds 350 and 455. Chevy has small 350. Olds, Buick and Pontiac 350's if not sure can be mistaken for big block motors unless you know what you are looking for. Though called small block, they are not small like the chevy. My 455 block destroyed the engine stand my brother used for years to build he 454 chevy motors. He was not aware of the weight difference.
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