After a few days spent fitting the stems and trying to get the fit nice and snug, I finally said to myself: good enough any small gaps left will be filled easily by the thickened epoxy.
The bow section of the keel was too stiff to form to the curve of the hull so I ripped it into two strips that fit nicely under the stem in what I hope will be an elegant scarf. I had looked closely at the plans where Ian Oughtred seems to show the outer keel glued on top of the bow stem. But the piece I laminated seemed to be easier to scarf in this way. The length of the glued surface is shorter, but I’m fairly confident the joint will be plenty strong.
The stern stem was a similar decision, however I did not have to rip the keel into two strips.