Labial pits are also not of taxonomic importance at the level that's being distinguished here...
I know you said "Most" but that's exactly what makes the heat pits meaningless, if they were important than Corallus would all be pythons and Aspidites would be boas. The Coronoid bone is the feature which distinguishes the two groups... not egglayers versus eggsacks, not heat pits, not new world/old world, not temperment... Just the coronoid bone.
"Genes, Like Leibnitz's monads, have no windows; the higher properties of life are emergent... And once assembled, organisms have no windows." - Edward Wilson, Sociobiology