I bought my 72 GT with the GM AC option installed, minus the console housing. For the nuts and bolts of it I like the setup better than the ARA unit as far as the engine compartment. The ARA compressor is a pain to take out and put back in, which you have to do to change a water pump, it bolts to the pump. Lots of brackets that have bolts only accessible from under the car. The GM unit has a couple of mounting brackets that bolt in above the alternator and also has a backet that bolts to the right side of the engine for an idler pulley to adjust the second fan belt. The compressor is a rotary type that is half as long as the engine. Before I blew a hose on the compressor, the unit would throw out super cold air from between the seats through an open hole. The evaporator is under a false floor behind the seats and has two screened air inlets on each side of it behind the seats and next to the doors. The hoses run under the car along the left frame rail up to the compressor. The condensor is mounted in front of the radiator and the dehydrator is mounted along side the brake booster. You must get another battery pan and rotate it 90 degrees to the original and a couple of inches away from the condensor. With the condensor installed, you have to cut a hole in the belly pan to get the battery in and out. A real PIA. You drop the battery down to the ground, then jack up the car to slide it out. The other alternative is to relocate the battery. I haven't had the false floor out in a long time, so I don't remember the setup there. A lot of stuff to do for AC. There was a thread on the classic opels site about a small compressor I think from a GEO that may work. You may want to check out that site for more info. HTH.