As I recall, he had some injury stuff happen between '68 and '72 and got away from steeplechasing because of it. After all this time I may not be recalling correctly but obviously I think I am.
As to the marathon, in those years it was not uncommon for track guys to try to make the Olympic Team in the marathon as a "safety" event in case they didn't make the team in their prime event. The marathon was not a high profile event then. Most marathon runners were guys who moved to the event because they weren't good enough to make national teams on the track so for some of the track guys the marathon was sort of a "soft" event., That would soon change but was still largely the case in '68. Billy Mills had done the same thing in Tokyo. I know there were stories floating around in '68 that Young wasn't actually going to run the marathon but the stories came to nothing.
Young was very, very, good and very tough and he stayed that way for a long time. Many people thought that he was robbed of a gold medal in Mexico because of the altitude. But he should be on anyone's list of all time great US distance runners.