The technical analysis paper that started Chrysler engineers interest:

https://digital.library.unt.edu/ark:/67531/metadc54614/

A few Hemi shaped cylinder heads had been built previously,
inspired by the ideas that a hemisphere has less metal surface for heat to leak out of,
or the valves can be bigger:

https://en.wikipedia.org/wiki/Hemispherical_combustion_chamber

“Cross flow, canted valve”
turned out to be where the “goodness” lay
rather than the hemisphere.

I admire all the Mopar Hemi’s
because each represents progress.

The Nissan NAPS-Z tweaks to the Hemi deserve respect,
as Bob Lutz acknowledges.

Bob Lutz lured away two brothers who worked at GM who were frustrated with their bosses who would not let them design a cross flow canted valve cylinder head with squish and tumble concepts to promote faster burn which enabled less degrees of ignition advance. Less degrees of ignition advance mean less “negative work.”

If a cheap way to make hydrogen is developed
expect the cross flow, canted valve, engine cylinder head will be further developed.