The plans suggest that the stems should be laminated as well, though after the fun of the full frame I was not looking forward to that prospect. Yanky book to the rescue again as it suggests that a sawn solid inner stem is plenty strong enough so I went for that approach.
The time spent with a hand plane getting the board edges perfect has paid off and the double spline joint is particularly pleasing to the eye - just hope I can keep up this perfectionist attitude for the rest of the boat.