The Star Wars Historical Sourcebook includes links to online videos at YouTube and Vimeo, so fans can see for themselves a visual source of information. Here’s a clip of Mark Hamill guesting on The Tonight Show Starring Johnny Carson on November 29, 1977, sharing a story in which Sir Alec Guinness plays a prank on Jack Purvis, who played the Chief Jawa in Star Wars:

https://youtu.be/DmyPxqOxOdA