273 to 340 swap in 64 cuda auto advise needed

guido said

I found this LH drivers side manifold on ebay
Anyone know if this will fit my 64 cuda

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That appears to be a B body manifold- as said, all bets are off if it's not an A body manifold. Some have made them work on later As, but definitely not a bolt in; and an early A would only be worse.