That sounds like it would involve a lot of digging and a lot of building - and I assumed the wall was built on top of some kind of foundations. Could the floorboards not be laid on top of that somehow?
It's a bit hard to see exactly what is there in the pictures but it looks like you have a hearth still in place, which is level with the floorboards?
I don't see how you can avoid breaking that out if you want to keep the same levels.
@ChasnotRobert started
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That sounds like it would involve a lot of digging and a lot of building - and I assumed the wall was built on top of some kind of foundations. Could the floorboards not be laid on top of that somehow?