Never used SSBC stuff, but those rotors look a bit on the small size for Autobahn runs. Unfortunately, with you being in Germany, your choices are limited. Years ago I was able to use factory parts to convert my 64 300 to 12" rotors, but I doubt you can find that stuff in the junkyard over there.

I will leave comments on the kit you linked to others who may actually have used the stuff. But I would suggest you talk to one of our members here, Dr. Diff, he knows his stuff as does AndyF, either one can point you to the right stuff.