For the total width, I ended up using the distance between the inside of the left bearing and the middle of the right inside bearing where it touches the Y rail (1065mm). When I used the outside of the left bearing to the middle of the Y rail (1080mm), it was overshooting the calculated offset by a small amount, but less than where I landed. Technically, my new value was slightly under, so maybe use the center of the left bearing?
Either way, in one shot, I can’t argue with this. This is performing the leveling and then running it again to see how close it is.
Here’s an 8 minute video if you’re suffering from insomnia.