YMMB FAC says:-
Low Visibility Operations NAVBL - RWY LGT spacing 90M.
So I guess that means 800m like you say.
The Airsevices charts on Ozrunways don't have any info about takeoff minimums or RWY LGT spacing. This info comes from either the generic AIP or the FAC if it's included.
Don't know about the reasons for YMEN.