The 1948 Gilbert HO Hudson is a DC engine so the prewar diagrams will not apply. The Pre-war HO engines used universal motors to run on AC and needed reversing mechanisms. Go to myflyertrains.net. The 1948 HO catalog is posted there so you can see the engine and trains sets. The Factory service manual is also the there and it has a DC Hudson engine diagram and parts list. The gilbertho.org site is also and the Gilbert factory service manual is cross linked from that site.