Cummins= the grey valve is 1 1/2". The actual valve is USUALLY reachable from under the black plastic cover under your rig. If you don't mind getting down low you can replace it with a pull handle just like you did with your black valve.
Go to any rv store and buy what ever brand they sell. The flanges on the pipes are a industry standard configuration for the bolt pattern.
Some claim that some valves are different. That may be true. Don't know why, because all of the flanges are the standard pattern.