If you attach the rod pipe(s) to the barrel, you will have to deal with the rod hole interferring with the tenon that attaches the stock to the barrel. Double barrel shotguns deal with the problem by creating a hollow tenon, or one in which the rod will pass through a tube right next to the barrel. But then the barrel slide will be very low on the stock. One needs to take into consideration the whole picture before deciding on individual issues. that's where a profile blueprint of the build comes to shine.
