In the very first pic,,,the last 1/4" or so of the bbl is tapered down slightly,,,
and the last little bit of the bbl inlet is tapered the opposite way,,,opened up.
A gap is the result.
I'd just glue in a couple pieces of wood at this point and re-inlet to elliminate the gap there and also the one at the end of the bbl at the tang.
The easier way would be to use some epoxy bedding mat'l and color it/ stain it.
Shape the area as needed when final shaping and darken it as it would likely be on a well used piece and no one will notice.
The epoxy repair will add some strength as well as be much simpler . It will allow you to move along with the project and not get hung up on a small detail.
Sometimes things like this can stall a project when we over-think the details.