I was away from Keighley when the film was made, but the rugby team colours would have been green and white hoops. Standard issue would have been the green/white reversible jersey. I don't know where the film makers recruited the runners.
The BBC adaptation in 1968, also featuring the winsome Jenny Agutter, did use members of the school cross-country team. She can mop my fevered brow any time she likes.
The film version used Haworth Prize Band, in which old boy Pete Greenwood played drums.
Your mention of Haworth Prize band brings to mind the story of the year they won the prize. The chara on which they were travelling broke down and after lengthy repairs they arrived back in the village very late. It was customary if the band had won to march through the village playing'Hail the conquering hero comes'. It was now well after 2 am and rather than wake everyone up they took their boots off.