What are talking about here your CJ I assume. Will your CJ do 70 now, I don't think mine will. Anyways I would imagine that it will ride a little stiffer, but you should be able to do it without any vibes. I wouldn't get real long shackles if you are getting new shackles. Make sure they do the dropped pitman arm, and extended brake lines if neccesary. Of course if you are going to bigger tires gears are probably going to be needed to give you engine enough advantage to stay at 70 mph. I'm sure you've already heard this but its not real hard to lift it yourself.