there is no problem with the existing break lines. you will need to fabricate or purchase some new ones from the master cyl, to the distribution block.
Unless the old lines are rusted or bent going to the wheels, they will all work ok.
I installed the SSBC kit and it went pretty well. The kit came with the lines necessary to connect the dual cyclinder to the distribution block. But you will likely need to fabricate or replace some of the brake lines. I had to since some of my lines were frozen in place. Overall, though, it is fairly easy to accomplish and is one of the best upgrades you can make to your car.