Other than replacing the brake lines, the only way that I know of to strike the brake lines off the list, is to use a tool ($) made for this. This tool is extremely hard to find.
The biggest problem I had with brake pulls on Mark VIII's came from a bad "lower" control arm. When you get it doing it regularly, back up real fast and hit the brakes. If the wheel pulls the other way, my bet would be on the lower control arm.