I agree with mobileparts. Drum brakes work fine if maintained. Where they don't work well is repeated braking from high speed (road racing) or riding the brakes on long down-hill runs, which nobody should do. Disc brake rotors cool faster. Drum brakes are also touchier to gunk on the shoes. The feds mandated front disks ~1973 because of uneducated drivers.
Before starting this, look at the prices for factory disk suspension parts. I see outrageous prices from PST, I think because of the rare lower ball joints. Perhaps you can find a different design from a company like Scarebird, Wilwood, or SS Brakes. If so, please let us know how it went.