The wobbles will probably stem from your wheelbearings or king pins.
All Sierras have a ton of steering play. You'l probably find that new shackle bushes will help more than a steering box R&R. With live axles, leaf springs and no panhard bar you will always have the feeling that there's a ton of play (and/or vagueness) because the axle moves around under the car quite a bit.
You should be able to find someone who will rebuild the steering box but IIRC Suzistore sell them new for $200. If I was you I'd find the steering box from a low KMs Jimny and convert to power steering.
