It’s news to me that the pitman arms are different.
I never worried about a different pitman arm( they look the same to me - I have one on the shelf I see no differences) + I removed and replaced at least 10 total -1961 & 1962 steering boxes during 10 frame off and frame on restorations and I would have noticed a difference in the Pittman arms when they were removed, cleaned and painted and reinstalled.
I converted a friends 61 Impala Hardtop just a few years ago from standard power steering to factory power steering - we used the standard steering box on the car and when it was done it drove like my power steering 62’s, I would have noticed any differences, since the conversion was done for a friends son in law, and it had to be right...
I know at least one of my 3 -1962 factory power steering cars has a manual steering box and as I said above i do not detect a difference between driving the cars. The one extra turn in the steering box I think is not noticeable when driving the cars.
just checked my cars...
factory power steering 62 Impala Hardtop 327 4 speed- steering box # 5666723( as I remember I think this was a factory power steering car)
rebuilt steering box on my 62 Impala SS 409 convert added factory power steering - box # 5666728
steering box on my 62 Impala SS 409 Hardtop- added factory power steering - box # 5666723
steering boxes & one pitman arm I have on shelf
# 5666723
# 5666728
pitman arm # 3741383A
I see no difference on the pitman arms after “looking at my cars today” - as I said above
I do not notice a difference in driving my 62’s( the 327HT and my 409 convertible) that have different part #’s on the steering boxes. Just drove both cars within the last 3 weeks
Paul