The bbls. were turned to a press fit at the chamber end and wasted in diameter until the last two inches of the muzzle end then both ends were tinned. Two holes were drilled & tapped for two grub screws into the fats and then the shotgun bbls were slotted and welded back up to the rifle bbls. That with the short length cut the weight considerably. I'm still looking as this is the second gun My Dad has done this way but I can't find a single picture of the turned bbls. Here's a oup;e more photos.

We unsoldered both ribs back to the forend lug then regulated the bbls.