I wouldnt even bother with the boomerang shackles. Even if they are not hitting the frame sitting when you hit a bump or even turn they will likely hit.  The best and most correct way to correct this would be to get a drop front hanger which could be welded on the 1" or so forward.  This would correct your shackle angles as well as move your front axle an 1" or so forwards giving you a better approach angle.  Then again if your gonna go that far then you mind as well do a rears up front setup.