Tom, I'm pretty sure the front calipers are not aluminium? But maybe the rear slave cylinders are.
The slider bolt question was thread size not allen key size (I have both key sizes in the tool box!) because I know Mk1 Golf sliders were M10 solid shoulder bolts, whereas Mk2 Golf / Polo etc with the same calipers (VWII 239mm) have M8 caphead screws which clamp down on a separate slider sleeve. So I wasn't sure what Roccos would have. Maybe it depends on the year. Guess I'll find out the hard way :)