My dad had an old GMC 550 they have owned many years. I really want to restore it. When it was new it had a V-8 with a Hydramatic that was equipped with a two speed gearbox behind it. The transmission has been removed, but the reduction gearbox is still in it. I was wondering what the trans looked like or what kind of numbers it would have had on it. It must have been a heavy duty unit for at truck that size. Finally, does anyone know how many large trucks like this would have been equipped with the hydramatic? Any help would be appreciated.