The 1968 GeGeGe no Kitaro anime wasn’t the first time one of Shigeru Mizuki’s horror manga was adapted for television. That honor goes to this 1966 live-action version of Mizuki’s Akuma-kun. The title character was played by Mitsunobu Kaneko, the year before he landed the lead part of Daisaku Kusama (known in the US as “Johnny Sokko”) in the live-action version of Giant Robo, one of the very first tokusatsu series I ever saw when I was growing up.
There’s a good article about the Akuma-kun live-action series here, at the Black Sun site: https://blacksun1987.blogspot.com/2009/12/akuma-kun.html
After a one-off appearance in a rare live-action 1986 TV special, Akuma-kun finally got a 42 episode anime adaptation in 1989, which also spawned two of those Manga Matsuri/Anime Fair mini-movies. In fact both of those movies have been subtitled by Inka-Subs, who have also subtitled more cool stuff like Galvion and the 1989 Jungle Emperor remake. Check out their site here: http://www.inka-subs.net/