They changed to mechanical clutch setup (not cable) as early as pilot HK's built in around September 1967 (nor sure if M20 in HR was mechanical or hydraulic), for use with M15 3spd and M20 4spd. Only the old crash boxes and mid 1968-1971 307/327/350 powered M21 4spd were hydraulic after that time (253 and 308 M21 in HT-HG were mechanical). Even the HQ MC7 were a complicated mechanical setup, not sure why the mechanical linkage setup was favoured after HR. They didn't use a cable setup until mid 1978 either and it was far superior to the old rat-traps or even the half cable, half rat-trap setup used in HX and earlier HZ.

When did they go back to hydraulic? Was it the start of 6spd boxes in HSV product in the mid 90's? I'm pretty sure my mate's 2001 GTS has a hydraulic clutch but I think the standard Holden LS1 VT, VX, VU or V2 has a hydraulic setup too.