Valves dont clatter unless loose or over reved (3000rpm would do that, but unlikely to be your issue) What you are likely to be hearing is spark knock. I believe your timing is either too advanced (possibly wrong timing mark, or other measurement issue, or the advance is not working. Another issue is fuel. If a 450 head and other compression enhancing factors like bigger bore, or popup (domed) pistons were used it might need 92R+M/2 Premium fuel. If you find fuel to be the issue, retarding the spark with a different cam plate in the centrifugal advance might be a way to avoid knock and use regular. Jim
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