Dude doesn't the frame start narrowing right in front of the body mount where the shackle tube sits, it would seem that the frame might interfear with your shackle on droop, run a longer leaf and put the shackle tube where it is on a factory solid axle to aviod an unnecessary head ache, my axle is 3" forward on a 48" leaf hanging off the stock shackle tube, I just moved the drop box forward for a good shackle angle and to keep my shackle from bottoming on the frame and body mount. I'm sure you got your plan laid out though so I hope it works out
