Is that a Woods 750 backhoe?
Regardless, if you check to see if it is roller chain or leaf chain, you can
buy a new length of the correct size at various places on line. If
leaf chain, any forklift supply outfit should be able to get it. If you
remove a few links, there may be a size stamped into the side of a
plate if it is leaf chain.
Leaf chain should be used for the swing, and it is much stronger than
roller chain.