Keel is cogent and personable here, although I don’t find his unexplained phenomena particularly unexplainable (red snow is caused by a species of algae, for one, and anomalous thunder seems to me a reasonable explanation for “skyquakes”). Letterman does a good job with the material and is funny without being condescending—the venue is The David Letterman Show, a morning show that lasted only a few months but won two Emmy Awards. (Late Night with David Letterman debuted in 1982.) Keel did not have a new book to promote at the time, and it goes to show how far into the mainstream the paranormal had penetrated.
The cast shown by Letterman and identified by Keel as a “bigfoot print” from New Jersey is actually a cast of a print found by a Mount Everest expedition in 1951. The print was found in snow and photographed by Eric Shipton, the expedition leader. A plaster cast can’t be made in the snow, and the party had no materials to make a cast regardless, so all reproductions were based solely on Shipton’s photos.*
I found some news reports (1975-1976) of the “Illinois kangaroo” here, here, and here. I did not find anything about police chasing a dinosaur in Italy, but I immediately thought of the Ray Harryhausen classic 20 Million Miles to Earth (1957).