I dropped them into place and found that they both needed some trimming along the bottom edge to achieve a good fit.
A few iterations with the block plane got us there.
Here are both panels in place, held with clamps and lead blocks.
They actually fitted better than I thought they would, but there was still a gap at the front which I would need to fill. Apart from that, it's a snug fit all round.
Here is the gap at the front of the port panel.
It will be easy to fill that with a piece of ply.
However, the test fit also showed that the cleat on the cabin wall was not thick enough to properly fasten the panel in place when gluing up, and offered little support.
So I decided to sister both cabin wall cleats before I installed the side panels. It's a bit more work but worth it to know the seatbacks are properly supported at the cabin wall.
Onwards and upwards!