I won’t disagree with you about Howard Hawks being the one who changed the ending of Red River. I will disagree though about the use of the term “phoney hate”. Wayne’s character was single minded in his efforts to move the cattle and while that single mindedness CAN be a good leadership quality it was obvious that the character was, to say the least, a little lacking in people skills. As I said earlier, he was an a**hole.
In addition you had very real animosity between the actors. John Wayne found out that Montgomery Clift was a homosexual and Wayne treated him like...well...like you can expect a 1940 John Wayne would have treated a homosexual. The bottom line is that the last scene where they had to act like they loved each other was the only scene that required acting.
No, every scene in the film required acting. Don’t fall into the trap of those who claim Wayne just was himself in his roles—that’s their way of detracting from his unique skill in front of the camera. He ignored both Hawks’ and Walter Brennan’s suggestions on how to play “older” and his acting here is of great subtlety, without the lurching and shuffling the other two wanted him to do.
It is indeed fake hatred they’re experiencing throughout the movie—on the surface, no, but in the climax we see when push comes to shove the Wayne character was a father figure who had no experience as such, so he just treated Clift’s character the way he would an employee. In the end, his turnaround makes sense, no matter how abruptly it’s handled, because when you look back it makes perfect sense. Wayne’s character is exhibiting tough love, before the term was invented.
Too much is made of Wayne’s disdain for Clift’s homosexuality. This is Hollywood, and Clift wasn’t the first gay actor he’d encountered in his life. The animosity between them was probably more about the excellent deal Clift’s agent (who was having an affair with Hawks’ wife) extracted, giving Clift almost as big a payday in this role as Wayne. Wayne and Clift’s problems were about Clift being a stage actor who looked down on movies, but before shooting started he realized Hawks’ wife was right, and he would learn a lot from Wayne. After saying Clift was “kinda queer” in pre-production, he was impressed at how such a man of slight build could stand up to his character. Wayne and Clift even went bear hunting together. Wayne even had Clift play poker with him and his buddies, but eventually what turned Wayne against Clift was not his acting or his “queer” vibes, but his arrogance as a stage actor who thought he was hot stuff.