Thanks Graeme....and the thoughts on the floorboards are appreciated as well.
I was a bit surprised when you mentioned the myrtle and questioned its hardness and suitability for the floorboards. I had not previously looked at its hardness rating; just found it quite hard and very easy to work. Anyway, the Janka hardness of myrtle is 6. This compares to 4.5 for celery top pine (used here for cleats and floors) and 11 for spotted gum which will be used for the mast step.
So will probably stay with the myrtle...just need my contact to come good with a stash.