Often a gun will go off face on the right barrel first, because it is typically shot so much more. Especially a gun that digests heavy hunting loads. I have had good results with shimming in a situation like that, where the bolting is still good. I often try first a tiny rectangle of HVAC aluminum tape. What I have seen measures .003", and has it's own adhesive on it to keep it in place. I put it on the hook. It won't last much over 150-200 shots before needing replacing, but will give an indication of how much may be needed to bring the gun back on face, and is quick and easy to replace. If you find that .003" is about right you can go to a more permanent shim, or even have the hook welded and refitted. Be aware that there is at least one well known doublegun 'smith who decries welding the hook. He has stated that in most situations the hinge pin should be replaced with an oversized one, then the hook refitted to it. A little research will show which 'smith that is, then you can decide whether you agree with him or not.