You've gotta do all things in proportion, have a look at the size of all the front end steering and suspension components and you really don't want to go too crazy in the brake and therefore wheel department. The sigma disks should pull it up well, mine work fine. people still use front drums for track use with great success. your front track is exactly the same. i can't see the r31 maddat setup being any real benefit over what you have. its still a single piston caliper and solid disk that is pulling up all of 700kg's.

Wurzel, if you have a twin res master, take out the little nugget at the base of the m'c which is made to hold pressure for the drums. its under the big nuts at the base of the MC