I had a copy for years, and Gato and Mancha were both Creoles, or Criollos. Morgans are very different in shape and action, bred initially as showy ranch horses for 'best' riding and still the stars of many American shows in both harness and riding. They are always a solid colour, whereas Creoles can be red or blue roan, or palomino, although their stock colour is dun. Criollos predate Morgans by nearly 200 years.
For anyone who hasn't read 'Tschiffely's Ride', it's a heroic account of Professor A.S. Tschiffely's ride (one horse ridden, the other carrying pack) from Buenos Aires to New York: 13,350 miles or 21,485 km. The horses were aged 15 and 16 and the journey was made in the 1930s, if memory serves me correctly. It's got a number of b&w photos showing the terrain, the ponies, and some of the people met along the way. Sure puts the 'endure' into endurance riding!