This technique has the advantage that even if there is a deviation from the centerline, it can still do the job, as the 'error' is reproduced symmetrically. The jig to achieve this is simple, but not trivial to set up. My first pass was not satisfactory, but a second pass was, and the glued-up transom is even now curing in the shop.
I spent additional time trimming the lamination for the internal stem (apron), and test-fitting it to the building frame, but I did not fasten it in, or do the trimming, as I need it as a jig to laminate the outer stem. I had previously cut and planed the laminations, so that was a matter of mixing up another batch of epoxy, and diving into the mess. That too is now curing in the shop.
Assuming the outer stem lamination works out, I'll clean that up and put it aside, then return to the task of fitting the apron to the keelson, and gluing that in, and then shaping and attaching the transom to the building frame.
About 3 hours.