Summit 383 Top Performer kit

So this was Summit’s answer if the 2086 Top Kit would fit on a 65 383 block. I’m still confused. What would it matter if the plug angle in original heads was different from 68 blocks on? The 2086 kit comes with new heads so wouldn’t be an issue. Is there ANY diffference in the 67 and earlier blocks with head to block bolt patterns?? You can see they say the 208622 kit is for earlier blocks and I assume they must have some reason to say the 2086 is for 68 blocks and up???
Mark me down as confused.
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