I gotta run out the door, but here are a few quick thoughts,
Flex isn't everything. Having said that, I hate, hate, hate the aftermarket poly C-bushings I used at first. They suck at allowing flex. I bought a set based on my original calculations and guesses on what my caster would be with my planned geometry and thank goodness my numbers were off and the stock rubbers worked fine (and allowed more flex).
An unexpected advantage of the ford radius arms is that I don't need an anti-sway bar. I drove that hunk of rust to Moab and back and never ever thought, "Gee I wish I fabbed in a sway bar".
Trying to tuck the arms mounting points up above the lower edge of the frame seem a bit over-kill, but I guess it depends on what you want and the design you come up with. I used Ford van mounts and welded them to my custom crossmember. They have hit stuff in the past, but never to the point where I might have gotten hung up (essentially it makes a nice ramp). It all depends on the terrain you wheel and how much perfection you want to design in. My truck was built with minimal money and minimal tools. Keep in mind that the higher up your rear mounting point, the steeper the angle of your arms will be. Getting your arms to clear the front of the frame might be tricky.