Reviving this thread after a few days -- I remembered that I'd previously done an analysis of AD&D 1st Ed. -> D&D 3rd Edition monster changes, particularly to the Daemons ("Yugoloths"), and I thought I'd link that here:
www.superdan.net/dndmisc/monster_changes.html
See, in 1st Ed. the Daemons were really fearsome. Part of the reason is they had this unique extra bonus to hit points, when nearly every other monster had just straight Hit Dice to roll. Some 1st Ed. example HD -- Vrock 8d8, Glabrezu 10d8; Mezzodaemon 10d8+40, Nycadaemon 12d8+36.
But then 3rd edition stepped in and gave Constitution bonuses (and more) to all monsters, and they stripped away the Daemons special hit-point bonus and replaced it with the Con bonus everybody else had. In so doing, Daemons lost all sorts of ground as on average other monsters received a +55% hit point increase, while Daemons seemed to
lose about half their hit points.
So based on my prior analysis, I made a few recommendations on what would be required to keep Daemons at their earlier place on the power curve. I computed that Mezzodaemons should be about HD 15d8+60 (127 hp, Con 19, CR 13) and Nycadaemons HD 18d8+54 (135 hp, Con 17, CR 17), just to put them in the right place according to 3.0 rules.
I notice that these are already more Hit Dice than Pants suggested in his conversions in the other thread. If demons and devils have generally been boosted yet again in 3.5 rules (don't have them myself), then that would argue for Daemons/Yugoloths to get even
more increases to simulate what they looked like in 1st Ed.
P.S.: Pants, you may want to consider more closely the 1st Ed. Daemon-weapon vulnerability. In the FF Mezzo- & Nyca-daemons say they are
not affected by iron or silver unless otherwise magical. In the MM2 they seem to say for other types that iron/silver plus magic is necessary.
