Okay - so I went a bit down the rabbit hole on the dual y-axis squaring. I flashed my config.h file with the new parameters to enable dual axis homing (lines 641: #define ENABLE_DUAL_AXIS and 644: #define DUAL_AXIS_SELECT Y_AXIS). Did some test runs, figuring I’d fake the second sensor by tripping the current Z sensor, and homing failed each time. After digging a bit, it may require a mod to the pins on the board, … and it may just not be possible with this board as @WillAdams notes.
@DanStory mentions in this post that he is running dual axis homing, maybe he’ll chime in with how he got it working.
I’m speculating it might require moving two pins on one Y motor to the D12/D13 pins on the board. But haven’t gone deeper than that…
And realistically, my machine is as square as can be with all the tests I have done. When i want to be extra sure - I do the crash method of powering on with the Y-axis pushed to full stop on both sides. So now it’s an exercise of “Will It Blend” curiosity.