57-59 GMC ch***is, going by the few clues I can see, such as the front bumper, dashboard, and steering wheel. I can't read the tag, getting a clear, large picture of that would be a help. Many of the old Step vans had bodies made by independent companies, and this looks like it's probably one of those.
P2503 is the model number, it's 137" wheelbase. I don't know if the year is in the serial number somewhere...GMC did not make it easy to figure them out. They used letter codes for the year, but I can't tell which letter means the year. N is 1960, but the rest of the truck looks like it cannot be newer than 59, perhaps they carried over the step van ch***is for a little while. Strange.
It looks a lot like a "Boyertown" body step van, but many companies were similar. The big tag above the one pictured should tell.
whatever the word is before "URBAN DELIVERY" on that tag, is the name of the company that made the body. I can't puzzle it out, but I expect you could if you took a real close look, and moved the plastic out of the way a bit also
Likely this thread will get moved to the "Antiquated" part of the HAMB where we discuss such things. It's not a Boyertown. Boyertown out of Boyertown PA tended to use Ford products. I have seen one of these before, not exactly like yours....not with the built up roof. This company used primarily GM ch***iss'. These are very interesting. Like Boyertown these vehicles kept their "late 40s-Early 50s styling well into the 1960s. If you notice this one has an "Advanced Design" type grille. The Boyertowns Kept the Ford F-1/F8 type grille well into the 1960s as well. These are actually very useful. They can do things nothing else can, many things. They actually surprisingly maneuverable. One problem though will be wheels as many had "widow maker" type wheels. More modern type 'Bud" wheels may be available. The wheel thing takes some research because not all multi piece wheels are "widow makers". You need to clean up those tags carefully with a wire wheel. They are not readable with all the paint on them.
I would not clean the tags with a wire wheel. I would use solvent, since they painted over the tags it was probably not painted professionally and the paint may just dissolve
The steering wheel was used on Chevy trucks from 57-59, I ***ume it was also on GMC s the same years. The dash is 55-59 GMC, as far as I can tell.