Gramp;
If not built out of sequence this gun should date to ca 1891±. This is a sort of transitional period for Lefever guns. Their 1889 catalog describes a gun having cocking rods & a side pivot top lever. Their 1892 catalog describes their "New" design, patented 1890, having two cocking hooks (one in the frame & one in bbl lug) & a conventional center pivot top lever. The locking bolt on the side pivot guns enters rib ext notch from the rear, while the bolt on the center pivot lever enters notch from the side. There are I know guns in existance having the "2-Hook" cocking but retaining the side pivot lever. All the cocking rod guns I am aware of had either the earlier thumb push or side pivot lever, but would not say for certain one does not exist with the later center pivot lever. It is also noted in the 1892 catalog the statement is made that ""We now braze "Both" the top and bottom lugs"". This leads me to conclude this was not always the case. In the event these bbls are not joined solidly at the breech by brazing you could be looking at a total refitting, more or less from scratch, considering the problems you mention. I would examine the breech very carefully for indication of a brazed joint.
