The columns collar/shifter od may be much smaller.
I know The 1967 valiant column is smaller and the inner cup of the mount neck that the rimblow wheel bolts to will barely go over the column. Like 5/8 larger .
But if the dart uses the larger column.. or if there are 2 necks for the early/late cars...then ..
No offense, and just a personal experience, but i had a rimblow wheel in my cobra jet ranchero, and hated it. Always honking when i didnt want it, couldn't find it when i needed it.
Of course, maybe the mopar version is much better....but i doubt it.