Sometimes They Come BackGoofs
The train accident that killed the greasers happened in 1963. The train that hit their 1955 Chevy, killing them, was the Southern Pacific 5021. The Southern Pacific 5021 was retired in 1955 and was the only train of its kind preserved and donated to the Railway and Locomotive Historical Society on March 8, 1956. It's not possible for that train to have killed the gang in 1963.
The headstones of Richard, Vinny, and North show that they all are born in 1946/47 and died in 1963 - making them 16/17 at the time. Wayne's headstone shows that he is born on the 15th of January 1948, which makes him only about 1 year younger than the evil trio. However Wayne looks like he is at least 10 years younger than any of the three kids.