I am by no means an expert David but.......... there may be some merit in moving the mounts 15mm out.
If you remember some of the earlier discussions & a little bit in the book about the
ideal rack length
It was mentioned that for the Escort rack to be ideal, it needed to be shortened a little
I am sure a man of your caliber will be able to move the mounting brackets safely
I would be reluctant to make longer brackets, although I suppose 5mm thick ones would be fine
Can't see it affecting the steering or suspension geometry a great deal, after all, most of us have made the rear track wider by 10mm each side.
That's my thoughts