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Although it is possible to squeeze 450 HP out of a 289, that would be really high back in 1964 and it would rather require an "upgraded GT40...
You could consider roller tipped rockers. They should fit without issues and reduce friction and wear a little. Not that I think that valve guide...
Perhaps the biggest giveaway that the first car is real is that it doesn't have the Le Mans stripes. A "cloner" would probably have added the most...