The beep is a geep that was rebuilt by Baldwin, It is a one of a kind locomotive.
The Beep was actually rebuilt by the Santa Fe. It was originally a Baldwin VO-1000, having it's four stroke De La Vergne 8-VO diesel engine with an EMD V-16 16-567BC engine. It was a prototype for a rebuild for Santa Fe's fleet of Baldwin locomotives, similar to their CF7 rebuilds. However, apparently the cost of rebuild was too expensive, so the Beep is a one-of-a-kind locomotive.