The only real difference is the size of the reservoir chambers. A disc brake reservoir is larger because more fluid is needed to operate the large diameter pistons of the calipers. The portion of the MC that operates the calipers will also need a much lower pressure residual pressure valve, 1 or 2 PSI instead of the 10 PSI or so that the drum brake wheel cylinders need to keep the cylinder cups expanded and avoid air leaks.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!