Great thread, again....
Your limiting factor is really only the tires and wheels.
I’m pleasantly surprised to see that without the mill hooked up that you’re under 8k on the rear axle. I’ve not weighted our setup but figured it’s right around 8k.
Like you, I’m not overly nervous about running that much on good stout OE rims and good tires, but before making a bunch of ad hoc mods that will only slightly reduce your rear axle weight, maybe just consider a set of 19.5s and be done with it. Can be found reasonably priced used periodically too.