If even possible, the repair process would be extensive, let alone expensive.
Just to speculate, I'd say that first, replacement sections would have to be sourced from the appropriate donor tubes. Then, the sections would have to be fitted to the holes before attempting the welding. Then, after the welding, the bores would have to be honed/reamed to insure a smooth bore. Next, the exterior would have to be shaped and the barrels refinished. Lastly, the gun would have to be proofed. (formally or informally). You probably would proof the gun prior to refinishing, just in case.
Just my opinions, it's up to the individual. Just the attempt process would be an interesting article.
Regards
Ken
