Isn't that cool, Speedy! "Upupa Epops", "Happy Jack's Go Buggy", and "Little Rebel" have that detail. It isn't actually where the rivets are, but where the spot welds are. When spot welding is done, you have to make sure the aluminum is absolutely clean, and in order to do this quickly, they simply brushed on acid which etched the metal, leaving behind the bright lines, and then performed the spot welding. Sometimes these lines can be easily seen in period WWII photos, especially from the factory. At other times, instead of just applying the acid where only the spot welds were going to be, the entire panel was treated (such as many of the cowl panels), due to the amount of spot welds, leaving behind a varied/pattern look to the fuselage panels.
If you look at the Flying Heritage Collection P-47, you can also see lines of acid etching on the bare metal.
While Bob Baker's "Sweet and Lovely" has gotten a lot of attention from the photographers over the years, my favorite of his two is "Little Rebel". A few photos of mine from 2010 and 2011. On "Little Rebel", I believe all of the rivets are even correct to the period spec (at least they appear so), as are all of the lock nuts and bolts. Just about the only thing it's lacking is the fuselage tank and original radio/battery in the back. It really looks the part.




