You can get a bracket to mount the Sanden style compressor without needing to move the alt and power steering pump. The compressor sits neatly on top of the motor. Same as VK Commodore had and late WB with factory air.
Why evaporator in the rear? For rear vents? Won't you need air flow from outside the car through the evaporator? It would suck dust if it drew air from in the rear wheel wells, unlike the plenum chamber.