I went as far as buying a control panel for a Euro W126.
The US ACC has a 5 or 6 speed (depending on year) resistor pack while the Euro control switch has 4 speeds. No big deal.
The US ACC vent flaps are driven by vacuum motors while the Euro selector switch pushes and pulls two cables. It wouldn't be so bad except that two cables can't easily be used to control 4 flaps.
Other issues like using a dual zone temperature controller in a single zone car are easy to resolve. Unfortunately you have to retain the ACC temperature control unit, which to me is no more reliable than the push button unit, so you can use the thumbwheel to control the heater monovalve and AC compressor.
In the end, you don't get rid of a lot of unreliable parts.
I wish someone would offer a manualized push button control unit. I mean one that ignores relative temperatures and sets the flaps based on the button pressed and cycles the compressor and or monovalve depending in proportion to the position of the thumbwheel. I'd gladly live with 3 blower speeds.
My living with 3 126s is a testament to the rest of the engineering because I would not put up with this type of ACC in a lesser car.
Can we talk about radios next?