The steel lines are secured by a bracket or mount to the frame and a flex line from the steel line to the wheel cylinder on the front. The same application would be used for disc brakes. However your original system uses a single MC and you would have to separate the rear line for the disc conversion. It would probably be better to wait until you get the disc kit and install everything at one time. It's likely that something will not match up otherwise.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine