disk swap on '74 or keep drums?

Drums have 2 disadvantages:
- They don't take as much heat before fading as discs.
- They will not work well if they get wet, like if you drive through deep water.

If you are not running in deep puddles or water, and not doing a lot of mountainous driving, then they will work OK. I have raced (rally) with disc front/drum rear combos and never had issues with adequately sized rear drums. And have overheated and faded disc/disc combos that were marginally small. So, discs do not always trump drums..... it all depends on how things are designed and implemented and the use to which they are put.

I don't plan to replace the drums at all my '62 Dart; it does not get driven or used hard at all, and they are generously sized.

You can get better shoe materials that will do better with fading on the shoes if you like; I used to get heavy duty (police duty) brake linings for racing from here:

http://brakematerialsandparts.webs.com/brakerelining.htm