Need help to ID this PS gear box

[Nima]

Hello:
I picked up this PS gear, pump, pitman arm and brackets long time ago (I am talking 10 years and more ago!) from local yard and I don't remember what model year chevy truck it was, 67-72 or next gen models. Based on what I have researched it has to be 1970s. I am about to finally convert to PS and I need a pitman arm and the nut which holds the pitman arm to the gear box. The nut on my current manual box seems to be the same size but it just doesn't start to thread on the shaft, so I am wondering if the nuts are different size.
The casting on the box is 7802644, and the numbers on the 4 bolt cap are 7812145 and 018 71.
Thanks for the help

[LockDoc]

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2WD or 4WD? Looks like those numbers cover a lot of different years and models.

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The 018 71 may be the date, 18th day of '71.

See if this web site helps any.

https://leepowersteering.com/pages/h...entify-gearbox

LockDoc
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[Nima]

Thank you LockDoc.
I have seen that site. It is very useful but unfortunately doesn't get it close to certain model years. If that stamped number on the cover is production year, then I should have taken it from a 71 chevy truck. That helps a lot.