ipdb says it was the alternate prototype with the transparent playfield that was too expensive to produce. This is because Gottlieb at that time was owned by Columbia Pictures, the studio that made the movie. I always thought Krull was in limited production, like Seawitch, but because the movie bombed.
Every thirty days there were anywhere from 5 to 10 brand new machines to play while they retained the successful ones and removed the rest, but they quit testing in the 90's at this location before the pinball business went under. in great quantity, Seawitch, Freefall, Goldball, a couple of empty clunkers that I can't remember. There were quite a few machines on site there that were not mfg. (now Betson International) and didn't realize it was never produced.
which served as a test site for Betson Pacific Dist. I played this machine in '83 at Mar Vista Bowling near Venice, Ca.