"I plan to turn the barrels off center at breech end to align rim with firing pins"

Just re-read the initial start of this thread. I would not go to the trouble of turning the barrels eccentric to the bores. Yes, it can be done that way, but it a lot more work. Just make the shoelump so that the barrels are offset to the inside. That way you can turn the barrels concentric like you normally would and braze them to the shoelump. That is basically what I did, only I made a monoblock rather than a shoelump. It will take some figuring to determine the barrel diameters versus the position on the shoelump, but that has to be done anyway.

Ellis