Given the broken stock neck, I wonder if this is one that would warrant the never heard of 'head transplant'? That way you'd keep the original beauty of the buttstock as original wood while regaining strength in the head/neck area. I think Mr. Travallion would be a good choice for that. That also opens up the opportunity for modern (your) dimensions.

The obvious fix for the barrels seems to be Teague liners. But, also an extra set of barrels from another Lefever would get the gun going quickly.