That makes no sense at all. Just because your drum brakes work "fine", that doesn't mean the car could not benefit by the addition of disk brakes. Everybody knows that disk brakes work better, will stop your car in a shorter distance, will not fade with heat as bad as drums, and are, therefore, safer. Yes, drums work fine, but when you add extra "GO" to your car, common sense dictates that you should also add extra "Whoa". And even if the OP does not add more horsepower, adding disk brakes is an awesome safety upgrade. I think @Dan's 72 is making a wise choice.