When Scotty is walking with his 2 friends, before the greasers chase him with their car, he says see yas later to his friends. You hear kids talking in the background. You can hear 'where is he.' That small sample is in the first 6 seconds of the Ozzy Osbourne song 'Mr. Tinkertrsin' off of his 'no more tears' album.
The locomotive that was used for the crash scenes that killed the greasers in the train tunnel scenes in the film, was the Southern Pacific 5021. A 4-10-2-type steam locomotive built by ALCO in 1926. It's currently on display at the RailGiants Train Museum in Fairplex, Pomona, California.