I hope you enjoy it and look forward to reading about your experiences. Earlier this year, when I had to be in the area for work, I managed to skive off for a day and walk from Tortosa to Xerta, taking a bus back down. It was very beautiful going up the river valley with the mountains on both sides, and the GR marking was good, although I didn't see many flechas. A cousin of my mother's was killed at the Battle of the Ebro at Gandesa in 1938, fighting with the International Brigade, and I believe his name is on a war memorial there (apparently one of the few loyalist ones not vandalised by the fascist rebels), so that will be worth seeing when I eventually do this camino, perhaps next year.