[Lew Silverman]

This is what I looked at, from the 1966 Chevy classification listing, for the 327-300 HP combo in Super Stock -

RHS Cast Iron heads # 12400 & 12402 accepted as replacement head

These heads may be used in SS only, not Stock

Dart Cast Iron heads with cast # 10021070 accepted as replacement head

This head may be used in SS only, not Stock

World Products Cast Iron heads with cast #'s 043600 & 043610 accepted as replacement heads - SS ONLY

(Formatted from Excel spreadsheet, sorry!)