I think they are the same, 66 or 67 will have the "normal" intake bolt pattern and bolts. They should have the really good small port, small valve heads, forged crank, and mechanical valve train.
66-69 had the normal intake bolt size and angle. All had forged crank and just the 64-67 had the mechanical valve train. 68 and 69 went to hydraulic and not adjustable.
