McCartney definitely played the 'red letter' game up, banning Big Red soda from store shelves, etc. It was a little forced, at least at the outset, but the game deserved rivalry status, at least for a 20 yr period.* It was useful that CU ascended as OU went through its dark age period post-Switzer. Same with KSU.
F Mizzou fans (my least favorite bunch from the old days). I have more impressionable memories of Mizzou football thanks to the hilariously bad Woody Widenhofer and Bob Stull eras. I know they had much more glory with Devine and Powers, but it certainly predates me.
* I suspect it is/was always a bigger deal for Nebraskans, particularly those in western NE, or the many expats in the Denver metro area, at least that's what I'm told by cousins.