Wow! Thats different and damn smexy looking. Most just run a tube between the rails, but your approach gives it some added benefits. Any way to run some 1/4" plate up the inside of the rails to the top of the new cross member? Kind of like how some R/A mounts hug the frame rails do.
As far as leafs inverting...The dropped rear leaf mounts change the forces on the leafs. The weight distribution is no longer split between mounts, and has shifted to the rear a bunch. This added stress, causes the leafs to lose their spring, and can bend them backwards behind the axle. The more you flex, the more they lose spring memory. Stock leafs for an explorer were not made for this type of abuse.
Going SOA will net you around 5.5" of lift with stock packs & shackles. resulting in 7-8" of total lift. This will decrease over time as your packs degrade.
F-150 mod (using the F-150 leafs, retaining the top ex leaf) will net you around 7-8" of lift with SOA, AND keep your weight evenly distributed on the axle. Benefits are, longer pack life, more clearance, and better pinion angles. Spring rate on this mod is good.
Better (and 5 times more expensive) spring rate & lift packs can be had from places like Deaver, OME. But you can get a whole bunch of bang for your buck with the F-150 mod packs,
Of course there is also the Chevy 63" leaf packs that can be done as well. Just have to move the mounts forward and back, to accommodate their length.
For me it is a simple thing of supply & demand. There are a ton of F-150's out there to get the leafs from, and can be had for dirt cheap.
bronco2guy did get hung up so bad at the beginning of a steep climb so bad, that we had to pull his rig off the rock. The shackles left grooves in the rock as we pulled his rig off. W/O them, he would have crawled right up.