oh gotcha
I read that wrong!
A hydraulic handbrake is not allowed for road use here. We have to have something mechanical.
Aren't the 17z discs smaller than the stock FL S8 fronts though? 330mm I think, compared to the S8's 345mm. People seem to use a 345mm Mercedes ML disc with the 18z too so also no bigger.
I have attempted to figure out fitting an 18z caliper to a 365mm RS4 front disc, but could see no way for it to work as the mounting lugs for the caliper and upright both occupy the same place, so I'm keen to see what you come up with. It would be much easier with radial mount calipers. That said, it might be possible with the ML disc. Just no upgrade in size, although the Porsche monoblock calipers appear superior to the S8 Brembos in pretty much every way.
It springs to mind actually that I don't think I've tried the 18z caliper with a stock S8 disc. Hmm...