Besides for longer travel struts (which I'm not sure exist for our application) is there anything we can do to increase down travel?

Are the struts ( and the fact that the HD springs keep them nearly fully expanded sitting in the parking lot) the sole limiting factor? Or, might JBA or other upper control arms help?

I've thought about measuring the height of the exposed threads on top of the center strut nut and putting a spacer that size under the upper mount. (so that the exposed threads would be below the nut rather than above). This would likely add 1.5" of down travel. I should have measured down travel before cranking that nut down, but always in a rush....... I do know cranking the nut down did not change the ride height.