The rear drums are narrower on most cars, and I think a different shape so wouldn't even fit. I had 9" drums on my 69 Dart and they stopped fine. Easy to skid the tires and that was a manual MC. If you want front disks, a 73+ setup will swap to yours, or Scarebird has a kit w/ new parts to fit 9" drum spindles.
Where drums don't work well is continual braking, like long downhill sections with tight turns where you can't rely on engine braking alone. That hit me twice, both on gravel roads where 1st was too slow and 2nd too fast to not tap the brakes on turns. After ~5 miles downhill, the pedal got soft (fluid boiled). Once in my Dart and once in my 65 Newport and it has massive 11"x3" drums. However, the DOT 3 fluid might have been old (absorbs water). Disk rotors have much better cooling.