The "how" is pretty well covered by the factory service manual. I think the problem is going to be where you get the parts.
The section in the 99 FSM is about 10 pages long. As far as I know, there is little or no difference among years except in the boost rate. It's a standard sort of Saginaw steering gear. You can replace the pitman shaft bearing and seals without rebuilding the entire gearbox.
I'm interested in sources for parts as well, so if you find anything out, please post back.