Pictures are worth a thousand words. As to bushings, they require a special press to remove the link segments to replace bushings/pins while usually the link segments are equally eaten up. You should have a master pin rail(chains), scan all the pins, should be one with a dimple or drilled recess to the head, or there will be a segment with no side holes and what appears to be teeth at a diagonal on it. The master pin will have to be the one to drive out to remove the rail, none of the others will do as the ears of the bushings protrude thru the segments in the next segment on all but the master link. If it is a SML or bolted master(smooth sides no holes) it will have to have the pad retainer bolts removed to get the link to separate. My Allis took a 20# sledge and lots of time to drive the masters out. Rails from Cat will run high, possibly to $4500(just rails) there are link measurements and wear charts usually in the service manual that if you decide to buy it buy a manual, are priceless. Aftermarket rails and shoes(pads) are available, check with local heavy equipment shops for availability and pricing, you will need minimally rails and shoe bolts/nuts, next up would be to inspect and or replace the bottom rollers and the drive sprocket rim or segments.
