I'm working on this, and have run into a slight problem.
I want to create a new closed point, KimRd, at the north end of the new segment. This would be where the Kimberly Road ramps used to merge into I-74. However, US 6 has a KimRd point farther north that was demoted eons ago but is still in use, current name KimRd_E. So if I created a KimRd on 74, it would break someone's route.
The obvious, if perhaps slightly less elegant, option is *OldI-74. I did that when I-35's mainline was shifted in Ankeny.
On the Illinois side, already existing Exit 2 (serving WB only traffic) will work for the end of the new segment.