2013.03.12 - UPDATE! - FAIL.......
The "low mount" rear PHB turned out to be a total FAIL.
Conceptually, it seemed like the mount would work and be strong enough. The severe angle of the PHB was a bit of a concern because I'd have to match it when I designed and built my crossover draglink... but I figured since I was building a custom set of steering arms, I could simply put them wherever they needed to on the knuckles.
So I put a 20* bend in the draglink to give me the clearance around the 3rd member, set the ride height and got the axle centered VERY carefully and accurately, then put a few tack welds on the PHB to lock the dimensions in place. It definitely helps to build the mock-up PHB with a slipjoint tube.... a couple tacks are easy to cut if you need to change the dimensions slightly.
Anyway, it took all of 2 seconds to see that trouble was brewing. I started cycling the suspension starting on the drivers side and didn't get more than 2" of bump before the upper link tower crashed HARD into the new framerail.

I lowered the DS and tried a few other combinations of bump and droop..... and after about an hour of misery I came to the conclusion that the low-mount PHB was never going to work right. The length of the bar was quite good (around 37" IIRC) but the angle at ride height was killing me. The PHB "grew" so much as the axle was moved upwards that the axle shift into the passenger side framerail was terrible... probably 2" of lateral shift in less than 6" of bump travel.
Unacceptable.
I was just about to throw in the towel last night out of frustration, when I had a moment of inspiration. "I wonder if that PHB bracket setup is symmetrical, and could be flipped to the front side of the knuckle instead?"
Check it out!
All the holes lined up perfectly, and the clearances were great. I didn't have to grind of modify anything to get it to bolt into place...
The main concern I'd always had with a front-mounted PHB is the clearance it would require to clear the pumpkin and upper link mount bracket. I didn't think there would be any way to put it up there without an ENORMOUS offset bracket, and I didn't think there would be any way to build it strong enough to avoid being snapped off under actual driving loads.
Once I threw the PHB on the flipped bracket, it became clear that I had PLENTY of clearance around the upper link bracket, so I threw a thick stack of washers behind the heim to simulate how much I could cut-down the bracket and still maintain the necessary clearances.
As you can see, I should be able to shorten that bracket by at least 1" and still be fine (the green taped part is my homemade "wobble stopper", I need to find a real source for those!

).
Here's the final shot from the DS that shows the overall layout of the bar relative to the upper link bracket, etc. (The PHB is bent, but obviously with this configuration it can actually be a perfectly straight bar).
Coincendentally, this ends up using very similar mounting points (z-height) on the axle and frame side as my very early PHB design when I was attempting to go over the top of the 3rd member. The PencilCAD data on this one shows that the axle shift under bump is minimal (maybe 1/4" toward the PS framerail under bump) and 1-1/2" toward the DS at full droop (both sides down).
The nice part about this one is that the frameside mount has nothing in the way of it, no link brackets, etc. So I can probably push it pretty far out there and really maximize the length of the PHB. I've got a lot of flexibility with the z-height of that PHB bracket too, so I can fine-tune that once I have a clearer sense of how the crossover draglink angle is going to end up.
So I guess, the night started off as a pretty frustrating time but ultimately ended up with a better plan to move forward.
-G