This is definitely not the quickest way to reach Ibagué from Girardot. But it does take you through some nice towns along the Río Magdalena on a mostly good and mostly unpaved road. The Magdalena is the problem. Several towns you pass through on the Girardot-Cambao Rd indicate the presence of a ferry crossing. These include: Nariño, Guataqui, and Gramalota. At least when we did this route, the only “ferry” to speak of was a canoe no wide or sturdy enough for a GS.
At Camboa, about 90 km north of Girardot, there is tarmac, a bridge, and possibly a toll. From there it’s about 20 km to Ruta 43 and then just under 100 km south to Ibagué. The best part of this detour is definitely the ride north along the river. Fingers crossed that you can find a way across without going all the way up to the bridge.