After much consideration, it seems like there's a right way, a wrong way, and then there's the way I'm going to do it.
Swapping out the four leaf springs for a 3 leaf pair seems like the right way. But would cost the most and leave me with an unneeded pair of springs to sell.
Cutting a leaf out of my four leaf springs (seeing as how I know nothing about how this is done or how it would affect the spring) seems like the wrong way, because I might spend a bunch of time just to ruin my springs, leaving me with one pair that is shot and needing to buy replacement 3 leaf springs.
Which brings be back to my initial plan of adding military shackles to the rear of the front spring and custom shackles to the front of the spring. All I have to buy is 4 military shackle plates (I have 2 sets of civilian plates I can customize and repurpose for the front of the springs) and hook it up. If/when either the front or rear springs end up sagging and I have to replace them, I can get the correct springs then and just remove my front shackle job.
It just seems like the shackle work is cheap, easy and reversible, and if it doesn't work it leaves me buying the new springs I probably needed all along anyway, and if it does work then I'm good to go until it's time for new springs.