This is digging up an old thread I know; I came across this thread and found the history lesson as interesting as the guns.
There is much discussion on the 4 bore here; on another forum I frequent there is a 2 bore double build that the gunsmith, Colin Stolzer, is documenting in video. I've been following this build for many months, the rifle is due to be completed next month once the regulation is complete. It seems that many that repied to this thread would be interested in this project:
2 Bore Jones Underlever SxS "The Double Deuce"
Cheers,
San