This went basically according to plan: I put 3 coats of epoxy on the underside of the two pieces, glued them together, and carefully checked its fit on the hull. I used lots of glue and temporary screws, working quickly to get it all done before the epoxy started setting up. Afterwards I used a router and a plane to trim off the excess.
This was the last major component to be added to the hull. The next steps are a lot of filleting on the cockpit, lots of sanding all over the upper hull, and glassing the entire cockpit and cabin roof.