James Doohan appears in this as a character called Chief O'Brien. James Doohan played Chief Engineer Montgomery 'Scotty' Scott in Star Trek (1966). His equivalent character in the follow up series Star Trek: The Next Generation (1987) and its spin-off Star Trek: Deep Space Nine (1993) was called Chief O'Brien (played by Colm Meaney).
This was James Doohan's first non-"Star Trek" film since Man in the Wilderness (1971) 21 years earlier.
James Doohan, Roddy McDowall, and Bill Mumy all previously appeared in various episodes of The Twilight Zone (1959).
When Peter Paul comes into his house at around 14 minutes into the movie, you can see pictures and a poster on the wall. One of those posters is from he movie "Rambo 3"(1988) which Sylvester Stallone is trained by Franco Columbu. There are pictures of body builders, and a few of them are of Arnold Schwarzenegger, who was friends, and a training partner of Franco Columbu.
James Doohan and Bill Mumy both starred in competing science fiction series in the 1960's: James Doohan was in Star Trek (1966) while Bill Mumy was in Lost in Space (1965).