Jeff,
The passenger coaches in service on the "Six Flags & Texas Railroad" were built by Six Flags Over Texas in their own shops in 1961 and 1962. To do this, Six Flags purchased old 5500 series Denver and Rio Grande Western narrow gauge stock cars. These stock cars were taken out of service on the D&RGW, had their tops cut off above the floor, and loaded onto standard gauge flat cars at Alamosa, CO for shipment to Arlington, Texas. Six Flags built the seats and roofs up from the old stock car frames. The trucks, couplers, and air brake equipment under the cars are still like they were on the D&RGW.
The two steam locomotives used to pull the trains were built in 1897 by Porter c/n1754 and Dickson (American) in 1901 c/n 1280. They hauled sugar cane in Louisiana until the late 1940's. They are still owned by the sugar plantation that purchased them new and have been leased since Six Flags opened in 1961.