I've never done it myself, but the S10 to G-body manual steering box seems common. Google g body manual steering box and you'll see a bunch of threads on various boards about it. Any 82-91 will fit. If I remember from my research, there was a split where I think the earlier ones had a slower ration than the later ones. I can't remember the year I ordered it for, but it was for the quicker of the two. Some people say to use the Regal pitman arm, some say to use the S10. I got an S10 one just in case.
Let me know if you're interested. Thanks.