The one Lefever & Ellis I have seen was as you described 8-bore. There is also one pictured on page 18 of Elliot's last book. These are muzzle-loader guns.
May not have been clear on my previous post but when I said I agreed with you on the Lefever/Dangerfield design was speaking of the SxS breech loader OWD was asking about, not the O/U Lefever & Ellis. So far have seen no evidence that either Lefever or Ellis had worked with breech loaders till after they seperated ca 1867.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra