yes the commodore uses drum handbrake inside the dome of the disc (same as r32 ect). this is the problem with hydros and r31 diffs, either have a cable handbrake or a hydro. unless you make custom brackets for other calipers.
if you want a 4.11, get a whole pintara diff, get a skyline 28 spline spool off ebay and some skyline axles, put the minispool in and swap the axles (would be a good idea to get new bearings, or at least use the races out of the donor skyline diff)
to answer your questions in the first post. yes, they are very strong diffs. the crownwheels very rarely break, its usually the axles that go first (very rare too). they all whine on the freeway, some so it all the time, some do it only on throttle. you get used to it, but don't bother trying to get it quieter. borg warners always whine
