fin box in today,
Here's the hole marked and some packers to keep the router level, instead of following the "V".

The routing didn't go super smoothly, I have a long drill bit modified to use as a router, but the sides aren't very sharp, and melted the blue foam a bit, so I didn't get the precise hole I was aiming for. No problem didn't take much thick bog to fill the gap.
The box was still a fairly tight fit, but to stop it moving, I've taped it up from the deck and weight it down from the bottom.
Next step, is to cut off the excess box sticking out of the deck.
Then fix the mast track and foot strap plugs.
But that may have to wait, until we return from NZ.