[basketcase]

That depends on the spindles. Used to be that all of the disc brake dropped spindles used the '71-'72 ball joints which are larger but now some companies have dropped disc brake spindles that go right on your '67-70 drum brake ball joints and also use the stock tie rods. Disc brake tie rods are also larger and the threads are reversed from the drum brake ones. If your dad gets the disc brake spindles for the drum brake trucks they will be a bolt on. As long as the ball joints are not worn they can be re-used.

Tom