As I am in the process of installing a new dual circuit system on my '51 3600 (drum/drum), I've been reading through the multitude of threads about what goes where. I've also read several articles in old copies of Vintage Truck magazine. A Google search led me to this site which has some really nice, simple pictures of the parts needed for the different set ups:
http://mbmbrakes.com/typical-brake-system-configurations/I thought I'd share it here to help others who might be in the same boat.