W2 heads

Well, these heads are for sale and the discussion between a potential buyer(not me) and the owner was that they are not for 340's. They are W2 natural race heads, cast iron, 48 degree, 47cc. I'm not familiar with W2 heads other than what I read here on FABO. So my question is what would make these not suitable for a 340 and what are they for then? Thanks -G

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