If the car came with factory air conditioning (a rare option outside of the deep south or desert southwest) then it is worth the effort to find the pulleys and brackets along with new hoses (custom made at a hydraulic shop). You can still buy a remanufactured Harrison A6 compressor. It will look better and cool better than a knee knocker aftermarket A/C.
If your car had heat only then you are better off with the aftermarket units. The hoses, vents, and air box under the dash are not reproduced. The A/C controls and the valves and trap doors inside the evaporator box are impossible to find and hard to retro fit.