L&R RPL lock swap, they lied to you.
Move the barrel back, cut off the ramrod under rib a little, drill a new lock bolt hole, a blind hole to perfectly hit the lock bolt fixture on the L&R lock bridal, grind off the back of the breech so the new bolt location can clear it, completely inlet the lock mortise for the flintlock internals and most of all send the L&R lock back twice to fix major flaws.
I could have done a sloppy job much easier but I wanted the touch hole at the perfect sunset centered position in relation to the pan and a minimum amount of shims glued in to fill any gaps. I did have to shim a gap at the tail of the lock, you can see it in the finished picture.