71 and 67 318 heads??

It should increase because you will have a higher comp ratio according to 340 mopar. I am not 100% familiar with the 67 heads, I know 66 273 heads are closed chamber, but not sure about 67's. Take a look at the underside of the 67 head, in other words the side facing the pistons. Is the combustion chamber a circle that is below the head surface or a sort of half moon shape that is flush on one side with the face of the head ?