anyway... to roSSifumi,
i have done before the mod u mentioned.
i used a 2WD eterna/perdana rear drum in disc caliper + disc. Bearing and hub cut out from the original drum so PCD remain 100.
so far no problem, there is improvement in brake performance just that be-careful a few weeks after the mod completion.
first my caliper piston jammed a day after the mod because the caliper was taken from a very old eterna....
after that... there was air bubbles in the brake hose... so i had to flush it twice before it was completely fine... (which caused me an accident)
so far its working fine... just that don't know why it makes some sound when the rotor is very hot... cool back down then its quiet again...