Depending on what rear axle you have. If you have the Ford 9" on your 84 like I do, you don't need to extend the rear ds with a 6" susp. lift, but it would be a good idea at some point if you plan to wheel it hard. If you have the Ford 8.8" you would need to get it done fairly soon, since the ds is much shorter.
AS for the brake lines, my SkyJ kit just relocated the stock lines, so I did not need to get new ones right away. I still plan on getting new ones, as mine are the original ones, and I think you get better stopping power for the bigger tires like 35's.