Dennis,
The rear brakes have self adjusters, but if you need to adjust them, remove the wheel and drum and punch out the slot in the drum, you can then adjust the brakes through the slot. You can use the existing rear line for a disc conversion. I usually run new lines to the fronts from the proportioning valve.
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