'William Hurt' wanted to play the role of Paul Maclean and once went fishing with Norman Maclean in Montana. When Hurt asked if he'd fished well enough to portray his brother, Maclean replied: "Well, Bill, you're a pretty good fisherman but not good enough to be my brother."
When grown-up Paul catches the biggest fish ever, and is washed downstream, the fish differs between a salmon and a large trout between scenes. The "tell" is the nose of the fish.
At the Labor Day picnic, the Rev. Maclean is playing horseshoes when Paul arrives. Paul addresses his dad by saying "Hello, Father." Although you can see Rev. Maclean say "Paul," the dubbed voice says "Son."
Shown in the bar mirror, Rawhide puts her arm over Neal's arm when she sets her drink down. When the angle changes to the actual actors, their arms are nowhere near each other.
Older Norman: [narrating]
That was the only time we fought. Perhaps we wondered after which one of us was tougher. But if boyhood questions aren't answered before a certain point, they can't be raised again. So we returned to being gracious to one another, as the church well suggested.