I run an adapter plate from Captain Fab to use a 69-up steering box on my frame. A previous owner had just used spacers but I continually snapped mounting bolts. The 79-87(91) have metric o-rings, but you can use them as long as you use a pump from the same year (or change fittings on your pump). Best bet would be to source the pump and box from the same truck in a junkyard. Whenever I pull one I also take at least the bottom half of the rag joint, it's easy to bolt apart and you get the correct spline count.
I like the metric boxes as they can integrate hydro-boost brakes very easily.
Adapter plate, it's intended for earlier trucks, but it works well on 68-down 4wd:
http://67-72chevytrucks.com/vboard/s...d.php?t=332923
I'll also throw one of these at you:
We all enjoy pictures around here.