Pan Am kept a pair of FP9A engines for their Officer and Crew Special (OCS) train. That allowed them to do their own track inspection, show off the line to visiting officials, and give a bonus ride to honored or qualifying crew members. They were supposedly acquired in a trade with Conway Scenic for ST 216 and MEC 252.
The FP9 series was built between February of 1954 to November of 1960, weighs 259,000 lbs and uses a 567C 16 cylinder diesel prime mover that develops 1750 hp, and 64,000 lb of tractive effort, and carries 1200 gallons of fuel. My thanks to The Diesel Shop for the information.