Wow, what an over complicated POS.
I understand why GM changed it. I have a 64 Chevelle, with air, and it looks nothing like this. I don't recall ever seeing an thermostat extension like the one in the picture.
Manufacturing has come a long way. No way this bracket would even be considered in the modern world. Pictured below is a modern Silverado Air-condition bracket.
It has one other piece a spring loaded idler, that's it.