Recently got the Nyambe: African Adventures sourcebook, and upon looking at the Classes section, I immediately considered dropping the presented notion of using the Custom Classes and Prestige Classes within as a replacement for corebook Classes. Using the right mix of Archetypes should do just as well.
Here are some notes I was considering.
-The Gamba Fighter: this version forgoes heavy armor in favor of mobility and dodging. While the Nyambe sourcebook says Barbarians are only found among Northern visitors, the Pathfinder Barbarian actually fits this class best, especially if using the Hurler (spear throwing), Savage Barbarian, Superstitious or Totem Warrior Archetypes.
That being said, a number of Fighter Archetypes would fit the Gamba Fighter well: the Archer, the Mobile Fighter and the Brawler. but I think it would be possible to create a Gamba Fighter Archetype, replacing bravery and some weapon/armor training levels with the Barbarian's Uncanny Dodge abilities.
-The Mchwai Wizard: more of an RP aspect here, but the demonization of Arcane Magic annoys me a bit, especially when it's set in the suggested rules. I'd just use a variant of standard wizards, trading in the spellbook for a Mojuba bag, with "bargains with Fiends" mostly a matter of superstition.
One interesting variant to consider would be the Elemental College wizard, representing Mchwai who bargain with Elemental Orishas for knowledge.
Alternatively, the Witch Advanced class actually fits the baseline Mchwai concept even better, as it's a class that depends on a supernatural patron for it's magical knowledge.
-The Nanala Rogue: Pathfinder Rogues with the right talent selection replace them easily. Nearly all the Rogue Archetypes would work, especially the Poisoner, the Scout, the Knife Master and the Survivalist.
-The N'anga Cleric: Both the Cleric and the Druid fit the N'anga role. The Cloistered Cleric archetype works best here for Clerics, as do a vast majority of the Druid archetypes, notably the various Shaman archetypes. The Orishas are already treated more or less as deities as it is.
Fitting the Orishas into Golarion should only be a question of deciding which Deity best matches each Orisha; Shanamu the Hunter is essentially Erastil, while Araku's focus on War and Smithing makes him obviously Torag. The Fiendish Orisha are less easily matched, though.
-The Sei Sorceror: born with the blood of dragons, just make a Sorceror with the Dragon Bloodline. More Bloodlines would fit Nyambe well; Abyssal, Infernal, Celestial, Elemental, Infernal, Undead, Aquatic, Dreamspun, Serpentine, Shadow, Starsoul and Verdant would work best within the setting.
-The Dembe, or "monster hunters", might as well just be replaced with Rangers. The best archetypes here would be the Beast Master, the Guide, the Shapeshifter, the Skirmisher (for non-magical hunters), the Spirit Ranger, the Trapper and the Wild Stalker.
-The Engolo, masters of unarmed combat, are just a different kind of Monk. The Martial Artist and Tetori archetypes would work best here.
-The Ngoma, or "drummers", are Bards who focus on the drums. The Archivist Archetype would be a storyteller who memorizes the unwritten lore of his people, and the Animal Speaker archetype would work well for a less powerful kind of N'anga. The Dervish Dancer archetype might also be justified.
That basically covers the base classes, but with a little creativity, different classes could work very well in Nyambe, like the Alchemist. The Oracle would certainly find a place in Nyambe society rather easily.
Whole lotta stuff
Okay, cliff notes version for my vantage point vis a vis yours.
Gamba fits more an alternate fighter, rather than barbarian, possibly with purloined rage feats and sanguar. The emphasis is on weapon training, to go with the brute strength, more than on frothing bloodthirsty rage.
Given the Nyambé setting has a justification for the hate-on for arcane, I find changing it removes a part of the 'feel' for the setting. I'd keep michawi specifically as non-good casters as they work with the fiendish orisha, even if not evil themselves. To an extent they seem more witchlike than wizardly, but that may be a flavor question for someone else to address. Also, the borozoi ability fits well with a level 20 ability for a witch, so it'd be another archetype.
Agreed on nanala.
N'anga are already basically clerics, and as clerics are of a base enough template to allow for a ton of customization, it's just a name change with a swap out of a few feats to allow sanguar. Also, druids would be n'anga to nature orisha, so no harm or foul there. A few specific orisha would be more suited to having oracles instead of clerics. That being said, while orisha are functionally comparable to deities, the worship of a deity is not mandated, so you don't have to map gods to the orisha...unless you want to have dogma conflicts regarding which name is appropriate, or having the faithful reach accords and have schisms based on their perceptions and approaches and interpretations about which names and faces fit best with the concept worshiped.
Mechanically, sei stay sei stay sorcerers, though the emphatic emphasis of dragon blood is not necessarily something I'd keep or mandate other than cosmetically.
Engolo would be tetori basically, with sanguar and without ki.
Soroko/poison oracles are easily approximated with poison master alchemists, with the minor change of spell types to divine from arcane.
Mask makers fill a niche closer to that of artificers in Eberron, so they would also fit as an alchemist kit in my book, with the masks' pigments and preparations being the alchemical end of things.
Zombi cultists are clear candidates for arcane caster status a la wizard or witch - again I'm inclined towards the latter over the former, with mandatory snakes. Witch doctors are also another templated witch, with maybe hints of being a witch/alchemist hybrid.
I still think Jaguar Cultists make for poor quality PCs, but I'm biased.
I'd do more, but I'm at work without my book or my PDF where I can get to either.
TL;DR all classes from Nyambé as archetypes of their base class plus sanguar where possible.