rear disc brakes on 8 3/4

Dr Diff does make a kit for the small bolt pattern, I have a set from him on my 66 Cuda. He uses the Cobra caliper with a park brake and a modified Toyota rotor. Probably not his most popular set but he makes one and it works great on my car, lots of track days no problem. Great guy as well!

Well there you go! Cass is great. Beyond just providing great parts, he's even helped me out a couple times when I had questions with an install. Knowledgeable dude.

As far as the old drums go, sure, they work. For the most part drums are plenty adequate. But there are a couple of situations they don't handle well. Water, for one. But that's pretty minor. The second is heat soak. Drums don't dissipate heat as fast as disks. So, if you're braking from high speeds, or braking frequently, heat builds up and they don't work as well.

Now, the OP is in Germany. Don't they have some fancy freeway with no speed limit? If I were gonna go run around on the autobahn, the stock drums wouldn't be my first choice...