Real deal about Track Bars; tire rub issue

[sleepyboy]

I have a '69 short step. I have done my best to assure my bed is centered in reference to the cab. The truck was lowered 3/5 but I bagged the rear to pull a trailer. In the bag application, I also changed the lower control arms and the bushings. I am concerned about my rear axle being centered due to tire rub and the inconsisntecy with bed to tire clearance on each side. I purchased a deluxe track bar and everything I have read says that a truck lowered more than 4 inches, may need an adjustable track bar. How do I assure my rear is centered? Is an adjustable bar needed? Do I need to take it to a shop to center it for my track bar application? I am also concerned about needing spacers. I know one of you gurus can help! Ed