I have one more catalog to flip through after I eat dinner, but I have seen literally hundres of pictures of emissions check valves and they all have 5/8" or 3/4" hose connections (suprised me), my dad was an auto parts sore owner operator for 30+ years, if he can't figure it out, it can't be done.
If it were me I would just cut the end off them and braze a steel nipple in them and away you go.(they cost $10 so even if you jack it up it won't break you)
Better still, braze in a 1/2 inch nat. gas line adapter which is flare to pipe, and use an AN fitting (AN6 I think) to connect it. BTW the threads are the same but the angle of the flare is slightly different in degrees of angle, but its low eough pressure that a little Permatex #1 will do nicely

From your friend MacGyver
