Jarabacoa to Constanza
The times that I have traveled this winding and very scenic mountain road with my own vehicle I did not observe what you would call public transport, ie gua-guas. However, there would be moto-conchos, cars (SUV's recommended), or pick-ups for hire in Jarabacoa. I would recommend the best place to inquire would be around the Shell gas station at the base of the route in Jarabacoa.
The transit time from the Shell station in Jarabacoa to the Isla Station at the entrance to the business district in Constanza is approximately 2? hours provided the weather and the road are in reasonable condition.
Regards,
PJT