I converted my 66' 230SL to rear disc brakes. I was hesitant at first but the disc brakes are way better than the drums. They just have so much better "feel" and they seem to stop better. The change over consisted of a replacement rear axle, I went from a 4:08 to a 3:97, I really was hesitant because my stock axle was a 4:08 and I didn't like the idea of higher gearing, but it was such a small change I really never noticed the difference except that now my speedometer is right on as I had taken the speedometer out of the car that had the 3:97 axle, so the speedometer is probably calibrated to the axle in these cars.
So, after my doing this job the things you will need are an axle with brakes; in my research I found that the axles on the drum brake cars are completely different from disc brakes, a brake proportioning valve; this is the very expensive doh dah that is above the rear axle and has the brake lines going to it to reduce the rear braking power needed to run 4 wheel disc brakes as the drum brakes are self proportioning by the wheel cylinder size. If you find a disc brake axle try and get this valve from the donor car if it has one. I serviced mine, they come apart very easily and are very simple and should be cleaned and checked if you get a used one. You will need the two rear brake hoses and all of the brake lines from the proportioning valve to the calipers. You will also need a master cylinder as those are different with disc brakes. While you have the axle out you will also need all the rubber parts like thrust arm bushings and donuts, spring pads, compensating spring pads etc. You will possibly need the pinion wrench and an inch pound dial reading torque wrench to set the pinion preload, this is a lot of fun. And while your in there you might as well put in new axle bearings and seals.
This is a big job and just doing it to get disc brakes, in my opinion is just not worth it. I had a sudden differential failure and had a spare disc brake axle and I had a spare drum brake axle. I decided to go the disc brake route and it was worth doing and the car does have much nicer braking.
I haven't seen any upgraded brake parts for these cars except for brake pad material, brake hoses, and drilled rotors. I went with stock pads as that is what was in the front and they were fairly new and all the pads should match. When I replace my brakes next time I may go with the more expensive metallic pads as I have seen those make a big difference on cars I have had that had crappy brakes from the start, but these cars have very good brakes, even the drum brake cars stop very good.
