1) Lengthen the beams as much as possible.
2) Angle the pivot bolt bushings so that each bolt points at its own radius arm bracket (opposite side). That'll allow it to droop fully, limited only by the shocks, radius arm bushings, & limit straps.
3) Angle the radius arm bushings down for more downtravel.
There was an Explorer done several years ago that had around 20-22 inches of travel from the TTB. There used to be an outstanding build series on offroad.com, but no idea if it still exists. They went into how to build the jigs and all the mods to make it strong again. Sorry, don't have a link anymore.
a prerunner bronco...doesnt sound like the greatest rig i would get something with A arms or you would have to beef up the TTB big time to withstand jumping and actually anything with the weight of a bronco. i would say get a ranger for a jumper prolly cheaper and easier to work on also.. but hey i could be wrong.
That pic looks strangely familiar, I've got a family friend out here in phoenix that has a buncha pics just like that, I think he either ran a Jeep or an Early bronco, let's see if I can find the pics.....give me a few days......i think it was a bronco though.