I just finished putting disc brakes on the front of my '50... I have done a lot of research on this. Most aftermarket disc brake conversion kits use the early 70's Chevelle rotor and caliper, and a sleve for the spindle. They also move your track width out .75 inches on either side. You can buy whole kits for 500 bucks that include rotors and everything, or partial kits that include just the mounting brackets and sleves. There are several companies selling drop spindles for 49-54 chevys, too.
Buffalo Engineering has a solution that does not interfere with the track width, and includes a drop in height, but you have to ship him your spindles and uprights. He uses the chevelle rotors, too.
Then you can do what I did... the " get low fo' no dough " route. It started when a friend gave me an old set of caliper mounts he had from a '49 truck. I re-drilled them to fit the car spindles, and then I got rotors and calipers from a buddie's junkyard, found a machine shop that made me a pair of sleves (free! 'cuz we got talking cars... I bought lunch, and in the end we just shook hands and said "see ya on Woodward"). Then I got uprights from a '53 off the internet for a few bucks (they sit lower than the ones on a 49-52) and put it all together. I also cut one and a third coils from the fromt springs for a total drop of 3". I had my sleve custom made so as to not change the track width, but I had to grind away the inner edge of the rotor and shave a little of the steering arm to get the clearance.
If I had it to do over, I'd save up my money and go with the Bufflao Engineering setup. Still, I can say that I did it myself, but it took me a while to do it. Spent less than a hundred though!