Hi Simon,
I run a Vacuum tank in Chris's green FC ute due to cam, Engineer prefered one was fitted. It has a Gemini Booster & VN Commo master Cylinder. Hard pedal feel was reduced a little with new reaction disc in booster and "softer" pads although went hard again on idle on subsquent applications at low revs hence the Vacuum tank.
PBR still have small tanks available although not listed - about $150 I think. If you want to try one out perhaps you can come down one day and we take the one out of Chris's ute to test your car (don't tell her about it
)
Trevor_B