The bell housing bolt pattern mid year in 65 prodcution from 5 bolt units to 6. Early 5 bolt bell housings will not work with later engines. The 351W should bolt right up to a 6 bolt housing.
As for 69 and 72 351w's check on the compression ratio, my book says cylinder heads were the same for both years, but who knows what heads are on it. It should have hardened valve seats. I can't imagine anyone selling an engine, pre 72 rebild or not, that was set up without the hardened seats. Block wise I don't know. I have heard that 351c motors cast before 72 were slightly stronger, but don't know it that is true for 351w. But if you are not going to be building lots of hp it shouldn't matter.
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