Listen there are several ways to do this, but use a little common sense. Putting any weight on or near the heater core is asking for trouble, your adding 2 nipples and the valve near the heater core. A gas valve is very hard to open and close because they never want it to close from vibration. So you may add stress to the core when you may need a tool to open or close the gas valve. My way is on a solid mount and the ball valve is easy to open and close and definitely no stress on the delicate heater core. By the way gas valves are available in ball valves also.