My '99 M750 has forks that I *think* came off an M600 of unknown year. I would like to simply make it a twin-disc setup up front, looks like the right side has the mounts for a caliper. Can I just find parts (rotor, master, wheel, calipers, lines) from any M600/620 or M750 that had twin discs and go from there? Is there more involved? Are there better options that bolt up easily?
EDIT: Despite searching, I didn't find the other thread about this same thing until after I posted this.
You'd also have to add a 16mm master to that list. So you're looking at a lot of work there.
As has been suggested in other instances like this...
You've got older, heavy rotors and (probably) similarly old pads. A much more simple operation would be to get your hands on a high quality rotor and matching pads.
It'll be a lot less invasive a job, and you won't be adding any rotating mass. If you get a lighter, better rotor the weight loss will help the all around performance of the bike, braking included.
A ductile iron rotor from Braketech and suitable pads will probably have the desired effect. Also beefing up the rear brake wouldn't hurt either.