Owners I have spoken to that have Vintage air in their cars all commented they thought the Air Con wasn't very efficient. I am generalising here and not limited to HQ-WB Holden's. All the units I have seen are very compact to try and get them to fit in small hot rod under dash spacers, and for that reason the evaporators are very small which would make them less efficient than most modern factory units.

When I fitted the Denso units to my Toranas I managed to control all the original functions,flap, fan and defrost ect using the original panel and cables controls. (everything look factory) The only addition you can see is a small push button switch in the HVAC panel for the compressor activation. Never had a Vintage air system but all I can say is on a 42 degrees day the hatch is a cool 23 inside which is impressive considering I have 1 7/8"headers and duel system only 50mm from the fire all and floor. and over 500hp engine, so the heat factor is all there.