Spaniard is a surname in the Cherokee Nation and the name Dick Spaniard sounds familiar. I'm not familiar with the Casto and Castillo surnames but I'll look. On Joseph E. Johnston's return from his expedition to survey the southern boundary of Kansas, a Cherokee named Spaniard guided them from near present Skiatook to Hudson's Crossing on the Neosho (Texas Road) in 1858(?).
I think there is a Spaniard Creek or Spaniard Mountain on the southside of Bayou Menard about 7 miles southeast of Ft Gibson. Driving south from Muskogee the turnpike crosses a small lake and I beleive the sign says Spaniard Creek. This is all off the top of my head.