The older 84-90 lower ball joints have a collar that threads into the lower part of the knuckle, that you have to set the height on. In 91 they were able to eliminate that.
There are a ton of brake generational differences, but as long as you stay in the same year, you'll be fine.
The difference I've seen in the draglink is the size of the threads for the TRE. I put an 88ish D30 on one of my 91s, and since I hate dealing with balljoints, I thought I'd just undo the collar, and switch it over that way. Nope. Different sizes, so I had to switch the TRE anyway.
What all comes in the kit? What all do you need to replace? RockAuto has fairly cheap balljoints.