Yep, I agree that this is a fantastic time to go ahead and not only replace your worn kingpins, but to get a disc-brake setup installed at the same time. I mean, you might as well do it now, while the whole front end is out of the truck, right?
Just find a '73-'79 truck with discs and take the entire front suspension, steering and brakes. Remove the disc brake components from the donor spindles, so that you only have the I-beam/kingpin/spindle combo. Drop those off at the local machine shop and have them install new kingpins (with bronze bushings, NOT the plastic ones!), and then bolt everything back into your truck. Here's a link to the disc-brake swap page:
http://www.fordification.com/discbrakes01.htm