From Trbiž (Tarvisio) to Cervignano del Friuli on Ciclovia Alpe Adria Radweg (at least first part)
http://www.gpsies.com/map.do?fileId=hqhvameyvtsbggri
There is a nice bike path from Tarvisio to Resiutta with just a minor obstacles (anotated on the map).
After Resiutta a quiet road is between Pioverno and Braulinus.
In San Floreano you can follow CAAR (unpaved), use alternative path (bad asphalt, small hills). On http://www.opencyclemap.org/ these two are marked with red line and letters CAAR (mainly asphalt) and blue line and letters FVG-1 or Ippovia (gravel). Or you can just follow the main road.
You can park your car near the train station Tarvisio Boscoverde (in a garage) and go back with the train from various cities/train stations on the way (Carnia, Venzone, Udine, Palmanova, Cervignano del Friuli). Just pay attention that the train doesn’t skip Tarvisio train stop.
embedded map:
kml file: trbiz-cervignano-del-friuli-caar.kml