I see on page 7 in the Handbook that:
65-69 200 1100 cc manifold volume
69-74 200/250 flat 1240 cc manifold volume
77-80 200/250 flat 1345 cc manifold volume
And also states that the C9DE - M has 1.75" throttle bore and a flat-topped log and that early 69 heads, C9DE - C,F,J and J casting are smaller 1.5" throttle bore.
So it appears that the later 69 heads were large log compared to the early 69 (1240 cc vs 1100 cc). Then in 77 went to 1345 cc so that must be the really large flat log heads.
At least that is how I interpret it.