Yeah! I was just about to say that those were not religions but I read my history book. As you may know the Incas worshiped( is it with double "p"?) mainly the Inti, but also the Pachamama and Viracocha (or wiracocha, same thing). But there were more religions in the Andes. My idea is that you could make a religion like "paganism" (similar to RFC europe), so that it could represent it.
Perhaps it could be possible adding as another Unique Power to the Incas something like religious tolerance, because when they conquered cities they accepted their god but with the condition they also adored the Inti.
I am not trying to overpower the Incas, but they were like that. Also, about the spanish conquerors, they only conquered the Incas not by having gunpowder or horses (huh, they were only 50 men) but convincing the subjugated peoples o join their cause against the tahaunatinsuyo. So, to represent it you could make that in the year were Pizarro arrived there will be a huge stability decrease. Remember in that time there was an Incan civil war to claim the throne, and because unstabilty makes possible civil wars, it will be great.
And yes, add me as a dev, I just recently registered (with lower than 50 employees lol).