I'm still waiting on he email from Supertrim. However in the meantime I've obtained a second quote from Veh-Quip.
Veh-Quip do not offer any bulk discount as "the job takes as long no matter how many they do."
The job involves dismantling the frame and welding a metal bar to the top tube. This bar has holes into which plastic lugs for the head rest locate. The headrest then slides into these. These protrude at the top and have a spring loaded detent for adjustment.
Veh-Quip will charge $121 per head rest (inclusive of GST) and will need the seat for a day. This is for a grey vinyl headrest. Cloth would be an extra $10-15 but they won't be able to match the Land Rover trim. You can either leave the seat back with them or leave the vehicle there.
Veh-Quip are at
27 Amay Crescent
Ferntree Gully 3156
Freecall 1800 302 432
Incidently, child restraints in Vic can just be put on the wheel arch, which is what I've seen in new cars but not what I heard from you guys in NSW.
I think there must be ADRs and NSW-DRs.
I'll keep you posted once I hear from Supertrim.