This is a pic I took last spring when I finally fixed my heater linkage, had to transplant cables from a parts car, along with a new bracket, the same broke one you have.
I took these from drivers side view, you can see things better, although I did take out the drivers seat so I could lay there and work things out in relative comfort.
That A part is what makes heat or not...I had attached a string to it to pivot it between hot and cold before I fixed it proper.
The part outlined in red is what usually breaks...it connects the linkage in a sliding fashion...seems overly complicated to me, but I didn't try to re-engineer it, just put in replacement parts...
I think why the part breaks is that the A lever gets stuck...when the vent foam material starts to dissolve, it sticks the vent shut...same thing happens to the fresh air vents...someone pushes the lever towards hot, it sticks they push harder and the part breaks...I sprayed lubricate all around the area to help witht he sticky problem, don't remember what kind...
Chris