I did this recently on my '85, and it was not a big deal. I did have some trouble getting the seal all the way down to the bottom of the track, but it fit very well. I remember using some WD-40 to help it slide down in there.
I did the beltline weatherstripping at the same time, and just like v737d said, the ones from J.C. Whitney don't fit too great in the rear, and the clips are not quite in the correct spot. But, considering I can get four from J.C, for the price of one from the dealer, I will stick with the Whitney ones. I had put a genuine Chrysler one on my '89 years ago and it fit great.