1979 GMC C1500 heat riser issue

HI there I have a '79 gmc pickup and the fellow I bought it from rebuilt the motor and took off some emmisions stuff (no big deal in IDAHO) but he also took off the heat riser vacuum and arm, the valve does not have the counter weight on it or the thermostatic spring so it just flaps around opening and closing on its own. I need to know which way to wire up the valve so as to keep it open and not cook that side of the engine. The tab on the valve can be pulled to the front of the truck or toward the back. Whick way is open.

Thank you for the time and help. Ryan