In the Godfather file that ships with Dramatica, Kay is cited as the OC/IC. To my way of thinking, the OC/IC should be listed as Vito Corleone.
What are the reasons you see it that way?
Because, unlike in the Godfather 2, Kay features so very little in Godfather 1 in which Vito makes many decisions with regard to Michael and also acts as his councillor until he inconveniently dies near the end of the movie, with yet more to pass on to Michael, as per his political contacts.
To the extent that Kay has an impact, it is to show the audience more of the more appealing aspects of Michael’s personality.
I’ll be upfront with you: I don’t think Kay makes for much of an IC, either. But I’m not sure I see Vito as a good replacement.
Can you argue that Vito is in the dynamic opposite role as Michael?
Wouldn’t Kay and Apollonia both be the impact characters, showing Michael glimpses of what a normal life outside of the crime world can be like? Both are innocent & playful and seem to show absolutely no interest in the world of crime.
In the beginning, Michael had no intention of joining the firm, but due to circumstances, his innate tendencies in spite of himself and the influence of Vito, he transitioned into the role of Godfather. Apollonia would show that he wasn’t particularly enamoured with Kay.
This. At the start of the film, Michael wants no part of the family business. Kay wants no part of it, either, which makes her a rather poor IC. The attempts on Vito’s life, on the other hand, draw Michael into his family’s world, until Vito dies and he becomes the new Godfather. It’s not that Vito is trying to get Michael to sign up, but it’s what happens to Vito over the course of the story that influences Michael. Also, the fact that neither Sonny nor Fredo can handle the business.
It could be argued that Apollonia represented Michael’s acceptance of his cultural fate, and that Kay remained as an influence via which Michael reaffirmed his original intentions, by claiming to Kay that he would make the family business legitimate within 5-years, so that she would agree to stay with him. That, however, would have been a very different objective throughline.
Well, let’s stick to the actual objective throughline, then.
What is it? What is Michael’s role in the OS? What is his MC role? What is Vito’s role?
Michael’s role is to become the new Godfather. Vito’s role is to protect, mentor and guide Michael to that end.
I’m going to nudge you towards framing what you said in dramatica terminology, otherwise we’re throwing aside the best tool we’ve got to talk about this.
Okay. leave that with me 
Vito is a pretty good option for IC i think. If Michaels problem is Feeling which I think fits just fine, then who is drawing him towards Logic? All of Vito’s sons problems are Feelings really. Sonny on one end of the spectrum and Fredo on the other. Vito tries to teach all of this sons to think business-like put all emotions aside.
Michaels feelings about his father’s business keeps him away but when his father is shot he wants his revenge (intense feelings) but he starts to solve problems like his father and thinks of the most logical way to enact his desire.
Later on, in a funeral scene, Vito continues to urge Michael to discover who the traitor is via logical means (who stood to gain and who stood to lose). In the end he completely abandons all Feeling and lies to his wife’s face.
“Never hate your enemies it clouds your judgement” - Michael (Godfather pt.3)
A significant problem with the Godfather is that it is a comedy about a bunch of knuckleheads who cannot cash in and move on to lines of business that are less dangerous. Beyond emotion, Michael, who already stands to inherit millions, has no compelling reason whatever, to become the next Godfather. If the other families had wanted to hobble Vito, they only had to eliminate Clemenza and Tessio, as they had done with Luca Brasi. The appeal to logic, as per the Corleone’s and the other families and their interminable strategizing, tends towards vainglorifying stupid.
Ouch! Don’t tell that to Coppola. He’ll send one of his cousins take care of you. 8^)