Disc brakes from my parts car

I have a 72 Dart Swinger, 318 parts car that has a front disc brake setup. I was wondering if there is any reason I should not swap those brakes for the drum setup in my 72 Scamp? I understand they are not as large ast the 73 and up but I figure a bird in the hand, right? Can you convince me that i'm wrong?
Also - on a related issue, there is a mild cam in my 360 and apparently I'm not getting enough vacuum for the booster to work properly. I have to pump the brake a couple of times to get firm pedal. Is there a remedy for this?
Thanks for your help,
Gary