The robot in the original Day the Earth Stood Still was the subject of urban legends, claiming that the actor in the suit was various celebrities, ranging from Captain Kangaroo to Ed McMahon. In fact, the actor was a non-actor, a doorman at a Chinese restaurant in New York who was very tall and therefor able to almost fill-out the robot suit. I think even then he had to stand on some kind of extended legs.
If you look closely at the Film, Gort’s “shoes” had something like a four inch lift.
In the scene where Gort is cornering the Actress and she says the famous line “Gort, Klatu Barrado Nikto”, you can see the ventilation holes under the chin of the costume. That is the only scene where they are visible.
That Movie and Forbidden Planet were two of my favorites. Earth vs Flying Saucers was pretty good and I really enjoyed when they did the parody of the Flying Saucer Attack on D.C. from that Movie in Mars Attacks.