I have been around these motors for quite a while and I have never heard of a difference between a 2v or 4v block - they are the same. The heads for a 2v or 4v on the windsor are also the same (1.78" / 1.54" valves), only the cleveland udes different heads for a 2v or 4v. Also pretty sure that the only 4 bolt main block was the Boss 351
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