What I find interesting about his work is that it's often easy to spot his source material. Not necessarily the exact image he used as part of the basis for an illustration. Just the source subject itself. Since Dieselpunk is a kind of alternative history, the use of thinly-disguised subjects can be justified.
Below are some examples, some of which I am personally familiar with ... for what little that might be worth. Image titles are either from various websites or are my descriptive ones. Click on images to enlarge.
A steam-powered transport aircraft that couldn't possibly fly. But who cares?
The Kalakala was operated in Puget Sound on the Seattle-Bremerton run by the Black Ball line. I never rode it, but saw it many times when I was young.
A Noir train station scene.
Although details varied over the years, Prohaczka's locomotive is clearly a GM diesel.
P-51 fighter planes, searchlights, what appear to be statues, and ...
I attended the fair in 1965.
Another unflyable device.
Prohaczka's image is of the Aerotrain locomotive. I rode the Aerotrain from Chicago to Detroit in 1956.
That's a dirigible, not a soft blimp.
But the source is clearly a circa-1910 Zeppelin such as this one.
A wartime scene. The large building in the background is ...
I've stayed there a few times.
Industrial designer Henry Dreyfuss designed the cladding for this iconic New York Central locomotive.