There are at least a couple of front disc brake conversion kits available that retain the factory drum brake spindles, Scare Bird and Dropem Stopem are 2 that come to mind. They use, I believe, 68-69 Mustang rotors and Chevy S10 calipers. I had a pair of 1977 Thunderbird front spindles and disc brakes that I was going to install on my 59, but man, are they heavy! Supposed to be pretty much a bolt on, but I heard from a couple of guys that either the track width or geometry was altered somewhat. I decided to buy a Wilwood disc brake kit, that retains the stock spindles.