disc Brake conversion

You will be able to use the stock upper ball joint used uup through 72 on disc and drum brake cars. I "think" you'll need the lower ball joint specified for the disc brake. As I understand it, the only difference between the drum and disc lower ball joint is the size of the bolts used to fasten it to the spindle (larger for the disc setup). If that's the case I suspect some reaming out of the mounting holes will have the same effect as locating the "more expensive" disc brake ball joint.