Not saying necessarly the rockers failed on 7 or 8 but was most often failers in those cylinders for no apperant reasons. Result was pistons and valves hitting. They were engines I didnt build. Some I redid heads on after the fact. Didnt get to see all the dammage. Speaking with Kirt Urban years ago on his advice began installing 3/8" coolant lines from the rear of the intake to the front crossover or in boat ran the lines out the transom sometimes. He stated lost many engies on the dyno without there addition. I had been doing it on SBFs for years. Also gasket matched coolant hole between the head and the block. One in the front right and one in the left rear. I do know this evened up temps between the cylinders based on plug readings and valve coloring. Sometimes thinking was the rear cylinders higher temps weakened the springs while the others still held fast allowing the 7 or 8 cylinders to float to a valve.

Personally I have truset Crane for the most part as they had done R&D for the big three as well as many other venues such as Mercury Marine. I also discuss cams with Engle for the most part speaking to them your speaking wit ha cam grinder not a computer jocky or program.