In the beginning I too felt it could be cylinder heads.
But there are more things involved here than the cylinder heads and I'm not at all convinced it is entirely heads. Look what RAMM has done with rockers, distributor and ignition on the "Cheepy". I'm not saying it is rockers and ignition in this case, but there are lots of other things that could contribute. We don't know what the cranking compression was. Spark plugs and plug gaps? Same plugs, same gaps?
How many ft-lbs does it take to turn the short block over? What did it take to turn the engine over with the valve train set up and the spark plugs out? I've seen different engines vary from 18-30 and 40-90 ft-lbs. Are those readings changing? How about the difference between a hot and cold engine? How much horsepower change from any difference before and during?
Are the the head rocker shaft heights different and does that change the valve lash when hot?
Brett Miller observed that there was some 6 degrees difference in timing required between the two heads. That is one whale of a different timing requirement for heads with similar combustion chambers. What gives there? A combustion chamber size of 4cc's?
What about a different fuel? What does that build require fuel wise? I believe I would be using a pump 91 octane with the cam and compression. However I can't know for sure, 'cause, I don't have cranking compression!
The future is going to reveal some interesting conclusions, observations and results.
Until then, I hope everyone is open and not entirely defensive through the process, on both sides of the cylinder head issue.