: I'm considering keel, shear line and
: accents. The rest will be WRC.

I'd forget the keel and use it at or above the water line where it will be more visible. About the only time anyone sees the keel is when the boat is being loaded onto the roof racks.

Does your plan call for external stems? If so the black walnut might go well there. Even if the plans don;t call for external stems you could always cap the ends with a thin strip of either that black walnut or the fir.

Just some thoughts

PGJ