I would favour Young too. Quarry excelled at handling big strong punchers, but struggled a little vs slicker guys like Ellis. I favour Young in a close competive fight.
In my "time machines are not allowed" version, Quarry beats him between 1969 to the end of 1973. Young would be seen as a tune-up / stay-busy opponent who was not a full-time fighter. Between 1974 and 1977 Young was at his best and Quarry was slipping fast. Young by easy decision during this period.
Jerry Quarry walked through Thad Spencer in that 1968 WBA Heavyweight encounter, even stopping Thad in round 12. Jimmy Ypung though a counter puncher would have a hard time with Jerry in his prime years. Jimmy does not have the punch to hurt Quarry, who would be pressuring and attacking the body of Jimmy, reducing any kind of mobility, slowing him down, cutting off the ring. Quarry by a very narrow decision, Young is not Jimmy Ellis or Muhammad Ali.
Jimmy Young was in Jerry's camp in the early 70's when Gil Clancy was training Jerry. Gil wouldn't come right out and name Jimmy in the '87 KO Magazine interview but Jimmy was one of the "experienced pros" that Jerry would regularly wobble and give trouble to in sparring sessions. Maybe because they were similar sized but Jerry didnt seem to have a lot of trouble with Jimmy in those days. Jerry did say that he had great respect for Jimmy as a fighter later on in the 70's when he was beating Foreman and losing debatable decisions to Ali and Ken Norton. Correction: I just re-read that article. He did name Jimmy Young as one of those "tough, experienced pros" lol.