I believe what you are referring to is one of the original disc conversion kits. From what I remember is that as you stated they used the original hub, generally with the the replacement bearing kit and a spacer. I believe the rotor & caliper is from a 73 up 4x4.
There are so many better kits available now from a host of suppliers that use a one piece rotor and lower profile calipers. I have installed them on TF trucks using the stock 15" wheels and had no clearance problems.
I wouldn't buy that kit. The booster/mc is another issue, I prefer the under floor conversion some like the firewall type.
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