50 year old American Standard boiler. Series:1BJ1, Boiler: GPH100. 125000 input, 100000 out put. Natural gas valve: JRVW600509. 1/2” natural gas piping. The boiler is on line and operational. Measured 3” of manifold gas pressure. Standing pilot. Looking for a new natural gas valve because of its age. Not sure if the existing gas valve is standard, step or slow opening. Any help would be greatly appreciated. Thank you.