As found on service sheet 459 for R3989 & R3990.
X6444 Hornby Spare Cylinder Block for Railroad County Class 4-4-0 Locos
X9468 Hornby Spare Cylinder Block N15 Class R2582 R2583 R2638 R2724 R2725 R2905
X7016 Hornby Spare Cylinder Block, Sliders + Motion Bracket for King Class R3332
