RR67GTO have the heads cc'd,or check the casting date.I believe there were 2 different casting dates for the 15's.1968(an advertised 10.5:1 on a 400) and again in 1970(an advertised 10.5:1 on a 455).In both application they were considered "Big Car" and possibly small valve heads.Maybe someone can shed some additional light,but have them cc nonetheless.The 9778822(9773322) presents more of a challenge.Do you have a casting date?Wild guess???64-66 vintage,Roger.
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