I have recently purchased an 86 K75 converted to an "S" model. It has a Works rear shock and Progressive front springs, as well as the "S" fairing and lower engine fairing. I only have one complaint, and it is about the very poor rear drum brake.
I decided to purchase the required parts and convert it to a disk brake. I bought an 85 K100 final drive, wheel, drive shaft, rotor, caliper, master cylinder and associated brake parts.
After reading on this thread that the 85 is completely different, I am concerned that the parts I bought wont work, though they look the same. I can't compare directly for several weeks because the bike and conversion parts are 2000 miles apart at the moment since I am on a cross country trip with My K75(S).
Any thoughts or information would be greatly appreciated.