Real self cocking Lefevers were made in four basic action types, rod cockers, two hook cockers & two versions of single hook ie small & large hook. Any possible interchangability will have to be between two guns of the same type.
That said I have a "Real" Lefever of the large hook type (the last & most common) which has a spare set of non-original bbls fitted in Italy. I likewise have 5 other large hook "Real" Lefevers of the large hook type. All of these have the adjustable ball & socket hinge joint. This extra bbl with or without adjustment of the hinge will fit one of the 6 without extensive modification, the one for which it was built.
