I pulled the engine from my 58 Viking, got to looking at the vacuum system, and I realized the cover to the vacuum valve that shifts my rear end is missing. I am hoping to replace the cover, but I can't find what part number this is. Anyone here have an idea? Or at least a flow diagram so I can use a different valve?

Pics of the valve.

https://drive.google.com/open?id=0B6Aw4aYru4MTS3ZyckZnSnlfS2c

The rear end is a GM 2 speed, I guess the valve is original.