Their settlements would be cobbled together near freeway on-ramps and they would all have persistent pneumonia and probably gout. Nobody who can build a bridge across a ravine without modern tools is involuntarily celibate. Inca laborers probably had their pick of partners, lol.
As I recall, the term "Inca" refers to the ruling class from around Cuzco, and as they conquered more lands they made the conquered people pay tribute by spending part of their time on labor. So the Inca laborers would just be regular people. But it's been a while, I really should read up more on the Inca Empire. Looks like there's a good youtube video on the bridgemaking.