Does your truck have a 5/8" hole somewhere in the middle of the firewall above the engine? If so that's where the valve goes.
The valve has a port with external threads that goes through that hole and into the cab for vacuum wipers and or vacuum gauge (if neither are used then it's plugged). A big nut threads onto this port to mount the valve to the firewall.
This may be a junk yard item...you would want the steel lines as well.
There should also be a "fresh air" line to the Hydrovac that connects to the high pressure side of the air chamber with the other end going to the air filter on top of the carburetor. these two lines parallel each other going down the firewall.
Mike B
