When The Time Tunnel first opens showing Doug and Tony on the spaceship, the music playing in the background was taken from The Day the Earth Stood Still (1951).
The silver outfits worn by the aliens were originally worn on another Irwin Allen series: Lost in Space (1965). They were the Robinson family spacesuits, altered by the addition of wide belts and silver skullcaps with cowls.
The language of the aliens is actually English played back in reverse. The original (normal) sentences can be heard throughout the episode. The aliens first line is composed out of: "from this moment on, you exist only" and "vulnerable points". The last aliens dialogue is composed out of: "that there are three alternatives", "primary test objective", "we have studies Earth from a", "has been located", "know its vulnerable points" and "you exist only as a convenience".
Two of the "homing staff" props used in The Revenge of Robin Hood (1966) are used as decorations on the spaceship.