Complex sentence: It was a three cylinder compound locomotive based on the second version of the CGR's Karoo Class and was numbered 900, but it was not classified by the CGR and was simply referred to as the Three Cylinder Compound Karoo.
Split into simpler sentences: It was a three-cylinder compound locomotive, based on the second version of the CGR's Karoo Class. The locomotive was numbered 900, but it was not classified by the CGR and was simply referred to as the Three-Cylinder Compound Karoo.