I ended up working on the design from the rough, more and more, until I started liking the way it popped against a sharp, digitized background. I decided not to have the original artist take it any further, and I finished the cover using the rough.
Here is the completed design image, with the title and author blocks:

Without really planning specifically for it, I got my Frank Miller-esque cover after all.
I built the complete cover wrap and uploaded it to Amazon KDP. I also did a final pass on the novel, cleaned up the front and back matter, and uploaded the formatted manuscript to KDP. I tweaked all the little settings for the release and ordered an author’s copy to see it in its final, physical form. I’ll get that in a few days, and if everything goes well…
IT WILL BE TIME TO PUBLISH!