If you are missing the shackles they are available now as reproductions (limited availability) they are pricey and missing additional pieces. Required hardware is shown below. Bolts are standard SAE, shims (some times as many as four) and locking plates inside cab behind seat pan. The rebuild bushings and retrofit is pretty straightforward. Your best bet is probably an ad in the Swap Meet.
https://www.flickr.com/photos/advance-design_parts_co/8129331043/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/8129483565/in/album-72157631868452754/