It has been published that headers will not work with A/C, this is an incorrect statement. Was is true, is that headers will work with either Stock or After Market A/C, but it is not just a simple bolt on up-grade. Modifications are required to the compressor and/or alternator brackets to achieve adequate clearance. The following pictures will show how I modified my alternator bracket to allow the proper clearance between the header and the alternator. A similar solution is viable for a stock system where the compressor is mounted on top of the alternator.
I purchased my A/C from Classic Auto Air which included the bracket you see pictured above. With this system, the alternator is relocated to a position above the compressor (opposite of a stock system) and the alternator belt is run off of the compressor pulley as is visible in the second picture. There were no clearance problems with the compressor but this was not the case with the alternator. In order to achieve the proper clearance, the mounting bracket need to be extended approximately one and a quarter inches. This was accomplished simply by welding two plates to the existing bracket, drilling two holes, and reinstalling the alternator. The orange arrows show the old location of the alternator pivot bolt, the green arrows show the new location. The next problem was installing the adjustment bracket. The old adjusting bracket had to small of a radius to go around the alternator so a chrome Chevy bracket was purchased from Auto Zone. The new adjusting bracket had the right radius but needed to be shortened and a new hole was drilled for the lower mounting bolt. The yellow arrow shows the new chrome bracket installed on the backside of the alternator.