the system used in the VB and early VC used the Harrison system. It used vacuum heater/vent controls and the evaporator box was partially mounted on the engine bay side of the firewall. It also used the much larger Harrison piston type compressor & an accumulator rather than a receiver/drier as used on the VC-VL. I'm fairly sure they also used an orifice tube instead of a tx valve which was used in VC-VL.
later VC & VH is very similar (if not the same). Air intake is in the centre of the plenum (on A/C models) The evaporator case was contained completely under the dash, the vent/heater system was controlled by metal rods, and it used a more compact & efficient Sanden SD508 rotary compressor.
VK-VL are different again. Vacuum controlled heater/vent, different heater/evaporator box, blower fan location, air intake on the passenger side of the plenum chamber.
I would probably recommend finding yourself a VC A/C system. It should be a straight fit into a VB (will have to drill a hole in the firewall for the A/C pipes) and it's a much tidier and more efficient system than the old Harrison type VB system
It's not as bad as it all sounds. My VH didn't come with air, I had to drag it out of my old VH, drill a hole in the firewall etc. I'm also going to be running the VR compressor setup, plus it will all be wired through the ECM (like the VR system). I bought a brand new condensor (still can buy universal fit condensors which is what the VB-VK used). And quite honestly, whilst it is a big job, there are a lot worse jobs. Keep in mind, most Commodores (apart from SL/E) weren't fitted with A/C from factory, the dealers fitted them to the cars.
The biggest problem you will have, is finding an evaporator that isn't leaking and/or twisted pipes from people who didn't disconnect the pipes with 2 spanners... Problem is early model Commodore evaporators were fitted in a sealed box. So if you can find a replacement evaporator core, you will need to cut the evaporator box open and plastic weld the box back together.
