It's wise to check what is actually the cause of the off face condition.
It can be caused by wear at the pin and hook, but also it can be the result of wear at the engagement of the bolting with the barrel bites. It can also be a combination of both hinge and bolting wear.
If the bolting and barrel bites are worn excessively, the barrels will not be drawn to a fully closed position, and this can lead to a gap between the barrel face and the standing breech.

You can check for hinge and hook wear by shimming the pin.
Ordinary paper is fine for this just to see if it brings the barrels back on the face.
You are not shooting the gun here, just trying to find what is the cause of the looseness.