Moment of truth today, peeled back the plywood. Looking pretty good I would say. A little messy around the edges in places but that will tidy up ok. There was one slight void left- that's the problem working blind- but I've filled that now.
Very happy that the hull is level on either side of where it cracked.
The crack at the foredeck was just a hairline on the outside, so I glassed that, and then decided to throw a bit of glass on the inside too. Not very proud of that particular bit, I should have sanded back a bigger area, but it hadn't actually cracked on the inside so in not too bothered.
Next job is the stern, but it's blowing half a gale here and the boatyard is very dusty, so I'm going to take the test of today off...