Best theory yet in terms of a figure.
What are the white blobs over his head?
Eyes.
I think Waltz41's colour image is as good as its going to get at this point in time. So the question remains what is the nose art all about? I think your idea (was "The Deacon" a comic book?) that you found is the right one. Could the figure in the foreground be a news paper boy? Could just as well be "The Deacon" with a brown Bible in one hand and a page tore out of the Bible in the other? Who knows? I dont think its a demon on the nose art because in the comic book they dealt with actual demons.
They dont look like the nose art.
http://fourcolorshadows.blogspot.com/2011/06/deacon-and-mickey-jack-alderman-1943.htmlBrief History of "The Deacon" cartoon.
https://www.markcarlson-ghost.com/index.php/2018/04/30/golden-age-holyoke-superheroes-1940-1948/As you can see in the above link they have all of "The Deacons" regular nemesis are listed and #1 is "Mr Death". Just a side note "The Deacon" was not even a deacon he was a gang member who donned the clothes.
So why do I think "Mr Death is in that image? The colour photo that Waltz41 provided has one thing that I can see that possibly matches the comic image of "Mr Death".
So here is a shadowy image of "Mr Death" Prominent eyes rounded head and the ace of spades emblem on his forehead.
Now on the nose art they have created a two tone blue figure to represent "Mr Death" this would give the image structure rather than a black blob.
When you take the colour image right on its forehead there is a shape that looks to be in the right place for the ace of spades logo when you follow the image down between his eyes there is a splash of pink there like the handle of the spade.
Sadly Charles G Pfost the pilot of the P-51"The Deacon" died in his mid air collision so we most likely wont be able to find the answers there.
His crew chief Emil Klein who is in the video of the plane taxing has passed away as well.
I say finish the skin with the colour image as is. Maybe one day we may get what we want and resubmit it it with the updated information.