I can agree to point.
The exhuast port didnt "really" make'm much better. It was the intake port.
Valve head size is the same except IV's where taller, tulip shaped heads, with taller/stronger springs and 1.65 rockers.
Strange they ran no better then 68 RAII's with 1.52's.
67-70 RA/RAII/H.O. d-ports did use stronger springs vs standard d-ports.
068/744 cams.
Also better exhuast man's just like the o-ports.
And of course different curved distrib's/jetting in carbs.