They didn't all have little valves. The "B" heads came from the factory with 2.072" intakes and 1.625" exhausts. Starting in 1973, however, the combustion chambers got bigger, and the valves got smaller, for emissions reasons. Still, even then the 455's had 2.000" intakes and 1.625" exhausts. Not huge, but they flowed very well. They also could be custom ground to accept larger valves.
Take care,
~Chris
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