1986 C20 Pitman arm Quandry

I received this email, and thought you guys will have the answer!

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Hello there im brian, i own a 1986 c20 diesel with the 6.2l. I have been having a hell of a time locating a pitman arm (steering box to rack) all my local stores and summit racing have only been able to provide a pitman arm with the key-way in the wrong position leaving my steering wheel 90* out of whack.
The guy at summit ran the numbers on the old one that was on the truck, and told me it was a nappa part number, called nappa-installed it and everything seemed perfect.
That is, untill about 2 weeks later when i regained enough play in the steering wheel to take your hands from the 9&3:00 positions to about 7&1:00 and vice versa.
I was hoping someone could help me figure out what the stock part number should have been for this pitman arm, so that i can find out if the previous owner just “made one work” or not.
I am going crazy chasing this issue, and currently its my back up truck and the only one running while i tear out and replace a wheel bearing on my 1991 k1500.
I would be absolutely grateful for any piece of advice i can get, and you guys seem like a good place to ask about these trucks.
I hope you had a great thanksgiving and i look forward to hearing back from you!
Thanks for your time,
-Brian