My understanding on this is that it was the HJ-HX change over as well.
This I believe was at the same time that the boosters themselves were changed from the straight input shaft to the bent input shaft.
I also assumed that the fact that HX had no drum front brakes anymore so no non power assisted cars anymore
that the old peddle to suit the power and non power systems was no longer needed.
HQ/HJ had the VH236 booster for drum front and VH262 booster for disc front which then changed to the HX onwards VH277 booster for the disc front only system.
Cheers Paul.