My largest wrench in the tool box is 1-1/8" and it is too small. What size wrench or socket do I need to remove the nut? Should I use an impact wrench, or will it come off easy (i.e. use an open wrench)?

should be 1 5/16"

On my 67SS it is 1 5/16.

I would use an impact wrench. I believe it is held on with 75 ft/lbs

The only socket I could find in 1 5/16" was a 3/4" drive (at Autozone). I used a 3/4" to 1/2" drive adapter and my 1/2" drive breaker bar with a 3 ft long "cheater" pipe on the breaker bar and a 3 ft long "cheater" pipe slipped over the pitman arm to break the nut loose. Then borrowed a pitman arm puller from Autozone and had to use both cheaters again to get the arm off. It was on the splines TIGHT. Thought I was going to break the puller.