Set up router table to cut the lower mortice, with stop blocks at either both ends to establish the desired length.
The key to this setup was that the fence was never moved the entire time the mortices and panel groove were cut, and the outside face of the workpiece was always against the fence.
I used a 1:1 template for the curve cut. Cut mated pairs together on the band saw and lightly sanded.
Next up will be cutting the tenons in the ends of the rails.
-- Pine is fine, but Oak's no joke!