You stated earlier that your info shows the pistons down .023. I don't believe this is correct. Especially considering what your '67 shows. Calculate the CR using .023 deck height, 75 head cc, .040 gasket thickness, etc. Would that give you the factory advised CR? I'm guessing it will be lower. I bet the .018 figure is closer...
I'm a hobbyist. Not a professional. Don't be hatin'!