Enos James (left) sidelever in the 1881 Folsom catalog

My ancestors only recently evolved opposable thumbs, but the left position is more comfortable for me

The very few Belgian fake proofmarks that I've seen are much more crude, and these look legit. And the barrels appear to be genuine stub twist, though I agree with Joe's observation regarding the 'browning' rubbing off at the breech end of the right barrel.
If one of our English correspondents could identify the 'AB' barrel maker, possibly it might be a hint as to the gun maker.