There is a guy in Maryville, TN that had a full scale Engine behind his home on an oval.
It was operational. 1970’s.
Legendary Disney animator Ward Kimball had a full-sized backyard railroad (with 500’ of track and a roundhouse) that he maintained from the early 40s until his death in 2002.
https://en.wikipedia.org/wiki/Grizzly_Flats_Railroad