The later model 9.9/15 carb will bolt on up to 1992. You could just use your roller and link instead of whatever is with the later carb. We are talking about dead idle here, so the cam should not be touching the roller and pick up timing is not an issue. I am not sure just what the initial needle setting is supposed to be on those later plastic top carbs, might be different than the 1977 spec.
And yes, there were several changes made that distinguished 9.9s and 15s during the years, but I don’t think that will affect any given carb’s ability to give an OK idle.
So, give it a try, will only take an hour or so…..