disk swap on '74 or keep drums?

Thanks everyone for the perspective.

I confirmed the rub is in the left rear wheel, where the shoe was making contact with the drum every time around. There's quite a bit of brake dust there, considering it's only been 1500 miles or so since I cleaned and lubed the brakes, but otherwise everything looked fine. I backed off the adjuster a few notches, but it will probably retighten itself next time I drive. I guess the drum is slightly warped. Replacing both rear drums and shoes is easy and cheap, regardless of what I do with the front brakes.