>>96004399
>each monster has its own individual morale score based on its ecology and behaviour
B/X says that? Could you point me to the relevant pages? I'm an AD&Dfag who got into the hobby using Labyrinth Lord, so my B/X specific knowledge is limited, sorry.
Pic related is what I found with ctrl+f

Besides, you can still backport AD&D's percent morale base to B/X's 2d6 morale base:
E.g. Troll
B/X morale: 10 (8 in specific circumstances)
AD&D morale: base 50 + 25 from HD + 6 from extra plusses = 81%

If you apply 81% to the probabilities of a 2d6 roll for minimum results, you get that 81% AD&D most closely correlates with 9 or less (83%) in B/X.