Getcha some backbone
The full size plans for stations 5 and the transom indicate that the keelson notch for the transom should be approximately 4 inches below the notch on station 5. Additionally, battens tacked to the sheer and one mid-plank landing project naturally to the transom landings to form a fair curve. Fiddling with the transom position with clamps eventually allows you to gradually adjust the transom until it approaches an optimal position. Check, recheck, and screw the angle brackets in. Done.
This morning I beveled the keelson landing surface in the transom notch with my dozuki and the 1 1/2 inch chisel, dry fitted the entire assemblage, and mixed epoxy (150 ml). It was too much by half.
Laminating the keelson from two pieces has the dual advantage of making it easier for the keelson to find its curve (which is quite pronounced at the transom), and making the whole piece stiffer as the glue sets. I made a plug the length of the daggerboard slot to help assure alignment of the two laminations and to keep squeeze-out from gunking up the slot. (visible on top the keelson at the very top of the picture below).
About 2 hours
The next phase is to bevel the keelson and the stem so that each plank lands fully and fair on the backbone, and assure that, on the stem, the planed forward surface is just narrower than the external stem, creating a pleasing reveal.
Each plank landing on the transom must be beveled to achieve the same full landing for the planks, which i anticipate being somewhat tricky. It seems to me that this aspect of the beveling must be done plank-by-plank, micro-adjusting so as to assure fairness. Should be interesting!