BB A body pitman arm
1-1/4" or 1-1/8"?
Just checked mine and it is 1-1/8" across the splines measured with a old fashioned manual caliper.
There appears to be a smaller spline box used on some of these cars. Do you know what ration the box is? I count 5 turns lock to lock on the 1-1/8" shaft box in my car.