I think you need to call ARB, something isn't right. There is either something wrong with the bumper itself or your LR3 may have had front end damage you we're aware of. I just relooked at the instructions (specifically steps 54-56) just to remind myself of what you are referring to and mine lined up with zero issue. I simply measure out the 815mm spacing and then my brother lifted the bumper and I bolted it on.
What you are describing sounds like there is something significantly wrong.
Update: After relooking at the instructions for a 3rd time, are you certain you have the impact absorber mounts mounted on the correct sides? Meaning the left one on the driver side and the right on one the passanger side? I'm thinking its possible you have them swapped which would lead to them being so far off as you're describing.
I had that thought, that maybe I had the impact absorbers on the wrong sides, but you can't put them on wrong because the cage nuts for the washer (driver side) and air solenoid (pas. side) would then be on the wrong side of the brackets.
I spoke with a tech at ARB and he didn't have any suggestions off the top of his head. He verified that I had the right part numbers, but really all that means is I have the right part number on the manual, not that the actual parts are correct. But as they do bolt up I suspect they are the right pieces. I emailed him a number of photos. We'll see what he says.
One way or another it will be on by the end of the weekend. I've got plenty of wire for the MIG if it comes to that