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B.M.B.C ,
You probably already know this by now since the thread is so old, before I got back to it, but:
I don't think the 267 is a good candidate. The bore is way too small to over-bore to 4 inches. Small bore engines don't have room for decent sized valves to open (they hit the block) for good rpm hotrod breathing, so you really do need a large bore for large valves.
This
link demonstrates this without me looking it up from my library.
Wes
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