[Will]

Just because the factory advertised a certain CC size for the chambers in a head doesn't mean that's actually what they were.

Numerous other heads show such discrepancies. Take '70 #13s for example - they are closer to 77-78cc than 72.

The ports in every small valve head I've looked at are definitely smaller than the ports in the big valve heads. It appears the factory was attempting to maintain a ratio between throat diameter and valve diameter, therefore the throats in the small valve heads are definitely smaller than the big valve heads and thus the bowls will be smaller also. The port from the short turn back to the port opening is about the same on all D-port heads I've seen.

The pushrod bulge really isn't a big restriction. The throat and short turn areas are where most flow improvement comes from when heads are ported.

Cutting the heads for larger valves should involve opening the throats up as well. This can easily be done at the same time as the valve job with the appropriate cutter. A little blending above the throat cut and a little work on the short turn will get you around 230 cfm flow, a significant improvement over the ~195-200 cfm of a typical small valve head.

A quick look under the valve covers should show you whether these heads have been converted to screw-in studs. Hard to believe that hasn't been done if the engine has a big cam in it.