Manual Master cylinder question

I have a leaking master cylinder ( 68 Dart GT manual with drum brakes) and I was considering adding a power booster to a new master cylinder. I have read somewhere on this "Brakes" category that I could use a master cylinder for a 74 Charger with manual front disc brakes as it has a larger plunger inside which acts like a "power booster" for the drum brakes......... has anyone else heard of this? I need to replace soon as the old master cylinder is leaking at the firewall and I want to repaint the firewall & aprons soon and do not want fluid leaking on the new paint !
Thank you !