It's nice to see photos of SP units from that era. In the 60's I worked on several RR's (interspersed with some military time and pursuing a college degree) as a brakeman or combined switchman/brakeman. Switch engines from all the major builders were in use, but I felt the best were the Alco's, whether HH, S-2, S-4 or S-6. In my opinion, nothing in RR diesel sound beats that of the normally-aspirated EMD 567 with its Roots blower (Geeps were also fairly frequently used in switching), but the Alco's were the best-designed for the trainmen climbing on and off, and were quick at building up speed to kick cars. They also had considerable pulling power: I recall taking 125 cars behind one S-2 from the Santa Fe First Street yard over to Hobart Yard. Granted, it's slightly downhill along the L.A. River, and the speed on those daily transfers was very slow (aggravating drivers on Downey Road as the evening commute was underway) but the little Alco's could handle a lot of cars.