I thought it would look good and be easy to construct them if I closed the darts with leather lace and grommets, rather than stitching them.
That turned out to be more work than I anticipated, so next time I think I'll just hand stitch them.
Since the hat has a somewhat funky look I'm calling it the Dodger, after the character in Oliver. I am pleased with the lines that it has, both in the crown and the brim. I expect to modify it slightly and offer it for sale at my Etsy shop as a steampunk top hat with attitude.