1 5/16" is the closest size I've got . As already mentioned , a "stout" air impact gun has always worked for me , when combined with sufficient supply of air. DO NOT beat on it , DO NOT use a torch ! . I'm sure you have used plenty of penetrating oil . A long 1/2"(quality) breaker bar will loosen that nut too.
The pitman arm may or may not come off easily , use the correct puller , some patience and more penetrant . Apply pressure with the puller , walk away if it doesn't budge , leaving the puller on with tension on it . Several attempts may be necessary. DO NOT beat on it.
Don't make me come over there !
Torque the nut to 185 ft/lbs