A formal link exchange generally refers to an internet based system that is set up to facilitate these sorts of link exchange. There are some well known link exchange systems on the web that are easily found via a web search.

This is such a sweet, vintage, tray puzzle. The child and his toys are kneeling beside the bed saying their bedtime prayers. The back is stapled onto the front and, in some places where not stapled, is loose. There are a few, small spots where the top layer of paper has scraped off. You can see the worst toward the lower left of the picture. The puzzle is 14" x 11". In the bottom, right corner are the words, "Litho USA".