You should have room to drill new holes on either side in the front shackle to locate the horizontal bolt further forward & the limit would likely be the distance between the front eye & the rear side of the front face of the front shackle. If you have the distance available & if you have to drill the holes center to center further forward than the .5" you need just to clear the current hole(s) then you can space the shackle rearward from the frame that extra distance. Keep tabs on the driveshaft end play & the angle of the rear shackles