HO RIVAROSSI #5456 4-6-6-4 Challenger UNION PACIFIC -UP 3716,4-6-6-4 Challenger Steam Engine w/Proto-Sound 3.0 (Hi-rail,Rivarossi 4-6-6-4 Challenger Union Pacific 3979 HO scale | eBay,RIVAROSSI HO 5457 Union Pacific 4-6-6-4 Challenger w/ Oil,Jaap Horst History of Technology page: Rivarossi Challenger