I made the following graph comparing an essentially stock original MR aluminum C5-H comp Cobra/GT40 head to the common aftermarket items. The -H head does not have any port work, other than a very minor blend of the seats into the bowl, and has 2.19 intake, 1.75 exh titanium valves. The aftermarket heads seem to be quite poor considering they've had 35 years of technology to take advantage of.
