According to some stats I read recently, the largest set of valves that can be installed in a Buick 401-425 ci motor (nailhead) is 1.92 in. and 1.50 ex., the same size valves (grossly speaking) that are in a 113 or G head 292 or 312
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The worthiness of a dampner is not only the correct position of its timing mark, but the condition of its rubber. Brittle, hard rubber wont do the job in dampning out harmonic vibrations. So if doing an expensive rebuild, finish it.