With the seat backs in place, I could now move on to install the transom cap.
This was a bit of a problem to deal with. It's fairly stiff and needs to be beveled on the ends to fit against the deck. As I was fitting this I discovered that I had beveled the top of the transom in the wrong direction (lower in back), so I fixed that first.
After a bit of trial and error I got the bevel right on the cap right, and with a set of helping hands secured the ends with a block and screw.
To fill the void under the cap and above the deck, I shaped an insert that I could glue in place. You can see here I cut it a little short, but a little thickened epoxy will take care of that more easily than remaking the part.
After gluing in the spacer blocks I glued down the transom cap and held the ends in place with three screws each.
I also glued the doubler under the cap at the same time.
After the epoxy cured I unclamped and sanded a roundover on both edges. Looks good and really stiffens up the transom.