Your identification of a car as Pullman Observation Dome 500 is puzzling.
Pullman owned-and-operated SLEEPING CARS were traditionally NAMED rather than NUMBERED. These cars had the Pullman name on the letterboards, and sometimes the name of the railroad or train which they operated in smaller letters somewhere on the car.
On the other hand, there were cars BUILT by Pullman, Pullman design, etc.but OWNED by railroads. These cars are usually identified by the railroad owner and a number or name, such as Santa Fe (ATSF) #500-505, built by Pullman in 1950, a series of lounge cars with a dome, bar lounge and private dining room (Turquise Room) run on Santa Fe Super Chief train.
These were not normally called "observation" cars, which usually refers to the car on the tail end of a passenger train where there is an open platform on old time heavyweight cars, or viewing windows looking toward the rear on a round or square ended modern streamlined car.
I am guessing that the Santa Fe 500 series are probably the most famous 500 numbered cars that could be called "Pullman" and "Dome"--but not observation.
Your BEST source would be the Pullman-Standard Library/Santa Fe which has photos of the car inside and out, both sides, etc during construction, side elevations, floor plan etc.
Here is my list of references to this particular series of 6 identical cars:
pix, plan "RR Mod Craftsman" May68 p.37
Dome 500 1960 Warbonnet1stQuarter 05 p.30
pix 501 "Santa Fe Diesels & Cars"(book) cover
pix 503 "Santa Fe Diesels & Cars" p.45
pix,plans "Santa Fe Car & Loco Plans"(book from 1950s) p.37
pix,plans #501 Model RRer Jul52 p.62
Dome 504 Warbonnet1stQ 05 p.30
general article on ATSF dome cars, Santa Fe Modeler, JanFeb82 p.20
pix, plans Pullman Std Library,Vol.1 p.121-126,XX.
color scale drawing ModRRer Aug93 p.81-87
pix, interior plan ModRRer Aug93 p.88
pix #500, "ATSF Color Guide to Frt & Pass Eqpt" p.15
CU lounge interior, CU bar ATSF Super Chief "Trains" magazine June74 p.7
Dome, photo Walthers HO model, review Warbonnet1stQ 05 p.31