Update. I took the pitman arm off today. I measured the overall length of the steering box shaft (2 1/8"), the length of the splined part of the shaft (1 1/8"), the length of the threaded part (1") and the width of the pitman arm body (7/8"). I also measured the length of the threads that were exposed (5/8") after I took the nut and washer off but before I pulled the arm back off. After calculating everything, I'm coming up with only 1/2" of spline engagement when the arm was installed and torqued to spec. These are the calculations I used:

2 1/8" (overall length of shaft) - 5/8" (exposed threads with arm in place) - 7/8" (width of arm body) = 5/8" (unused splines at top of shaft)

then

1 1/8" (length of splined part of shaft) - 5/8" (unused splines at top of shaft) = 1/2" (of splines covered by arm when in place)


Should be more than 1/2" engagement, shouldn't it?