I bought a Klutch torque multiplier from Northern Tool:
to torque my Kurt hitch ball to the recommended 450 ft. lb. (I don't trust mechanics with air impact drivers either.) It worked well enough but being able to put the draw bar in the receiver provided a pretty good "vice" to get everything into working position fairly easily. Keeping it on a lug nut might require three or four hands.
The Klutch ratio is 3 to 1 so calculating the apparent needed input torque is easy, but the instructions state: "Due to frictional losses in the gear train, a torque loss factor of 10% to 20% should be anticipated." So you can get a lot of torque out of it but accuracy is not a strong point.
Northern also sells a 3/4" drive 40" breaker bar that may be all you would ever need.