[kehstr]

i believe it was right around 78-80 when they changed to o'ring lines, and you will not need the o'ring style. Gm put these boxes on all trucks, suburbans and full size blazers from 67- about 78-80 like i said before. Make sure that you get the appropriate 2wd or 4wd box for your truck. 2wd boxes have a place for a nut to hold the pitman arm on. 4wd don't, they just have the splines, the pitman arm clamps on and holds it on with a bolt that goes through the pitman arm. You can look at your current box to get an idea of what i mean. If you have a 2wd when you put the new box on, you will probably not want to even deal with pulling the old pitman arm off, it will be better money and time spent to but a new one and put it on. If you have a 4wd, then it's easy enough to pull them off, and they aren't a wear item, so just reuse them.