Indirectly alluded to in 'A Waltons Thanksgiving' (1993)
The (apparently) next-to-last Waltons movie, set in Nov. 1963 (ironically, about the same time as the release of "Spencer's Mountain").
Although much of the storyline is taken up with the JFK assassination, there is quite an extensive subplot about John and Olivia's plans to move out of the old Walton house and up to "the dream house on the mountain we've been talking about for years."
In the end (big spoiler hahah) John and Olivia decide they want to stay in the old house.
Would have been funny if John and Olivia had mentioned something about seeing a "movie about a country family building a mountain house" and laughed about it.
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4) You ever seen Superman $#$# his pants? Case closed.