Chris,
yeah, the hull looks pretty good I thought.
I'm thinking about cutting the cabin sides at just below deck level, then the deck will help maintain the cabin shape and once bonded to the lower/old section, plus too the deck, it should be strong enough and water tight (deck to cabin).
If I cut the old sides down to deck level, I will have to insert small sections of sheet brass or similar to maintain the shape between between new and old.
Once I have cut the old sides down and before fitting new ones, I will then fit the new shaft and do as much inside the hull as I can whilst access is better.
I think that's the plan, at the moment anyway.
Will