An added comment to my lobbying for the part of Aguirre...
I think I figured out the solution to our problem about who is going to be John Twist. Stay with me on this, it could actually work and it would be really cute and everyone wins.
See, what we do, since John Twist just sits in his little chair and never goes anywhere... we get a dummy and we just put him in the chair and that is our John Twist. Then everything that is said to him is phrased in the form of a question and Ennis and Diane Twist wait through an awkward pause where he just seems like this huge jerk and then carry on the conversation as if he's just an asshole that plays those silent treatment games and/or speaks in his own sort of language of grumbles and facial expressions.
For instance... the scene could play like this...
ENNIS: Do you know where Brokeback Mountain is?
[awkward wait]
ENNIS: So, you thought he was too damn good to be buried in the family plot?
[awkward wait]
ENNIS: So he's going in there, hunh?
[awkward wait]
ENNIS: Well, that's okay, sir. I understand.
So, we could play it like that... or if you want, we could actually just change the ending altogether and let John Twist be dead and Diane Twist gives Ennis the ashes and they have a moment in the kitchen and everything. Tears, tears, tears, cherry cake to go around. Ennis is her newly adopted son and promises to come back every Christmas.
Just some thoughts.