That is very close to what I plan for from a barrel, buttplate and potential trigger guard perspective, just for now in half stock to make barrels interchangable.
There will be no set triggers, no fancy wood and of course no sliding wooden patch box.
The idea is to make it also interchangeable from flintlock to percussion, so the lock choice is a percussion and flintlock with the same lockplate.
Most likely a lockplate without the fancy pointed end, but a mortise a 1/4" or 3/16" router bit can be used for.