I'd weld a bit of flat onto the side of the oxford bracket, flush the joint and drill two new holes. With a bit of careful welding you could fill the two original holes, flush them off, and paint the "new" bracket black. If done well, it would not look makeshift. If you aren't confident, post it me and I'll do it for you.
Another alternative would be to get some sheet stainless and cut it to the new dimensions.