If you're using old Rivarossi/AHM streamlined cars, you can use sides from Brass Car Sides to create different cars.
http://www.brasscarsides.com/
Probably the three-volume "A Century of Pullman Cars" by Ralph L. Barger was the most complete study of Pullman cars, including Palace (wood) cars, heavyweights, and streamliners. Going to Amazon.com and searching "Pullman car" will come with several books on the subject.
It's long out of print, but Walthers came out with a softcover book of passenger car diagrams (showing exterior and interior drawings) that I use a lot. If you find it on ebay or at a RR flea market, it probably won't cost much.
Mainline Modeler ran a series on Pullman cars, beginning, I think, with the January/February issue in 1981, to at least the September/October issue in the same year. The latter one promised a look, sometime in the future, at parts suppliers for the various scales.The series was directed at Rivarossi's 12-1 Pullman, but was also useful for other passenger cars available at that time because it showed and explained to some degree the various air conditioning systems and other underbody details.New England Rail Services offers styrene windows and other details for doing these conversions, and PSC offers detail parts, in styrene or brass, for passenger car underbodies, such as brake gear, generators, etc.
The Rivarossi heavyweights were the predominate r-t-r full length cars available at that time, while Walthers offered a wide selection of full length heavyweights in kit form, including most versions of the Pullman cars seen on the real railroads.I wasn't too interested in modelling passenger cars at the time of the articles, but found the information, photos, and drawings interesting enough to hang on to, perhaps for future use.When I finally got around to passenger trains for my free-lanced layout, I realised that my road wouldn't have had need of any Pullmans, unless they were run-through cars from another road. However, by this time, the Rivarossi cars were showing up on the used market at prices I could finally afford, and I bought them as they became available.
I made several of the 12-1 cars into coaches, usually with a few sheet styrene partitions, window shades, and Pikestuff seats, along with the air conditioning ducts available from NERS:
However, I spent considerably more time on the underbodies:
I did convert one of the 12-1s into a solarium car, using a NERS window kit...
...and changed their combine-with-not-very-many-windows into something more commonly seen around here:
The combine was also a good starting point for "The BEE", a diesel/electric doodlebug (formerly a gas/electric):
I left the Rivarossi diner pretty-much as-is, but with more details:
...and converted another diner into a combine by shortening it:
The Rivarossi coach, with the roof from their RPO, can be made into a fairly good representation of the CNR's "mountain observation cars", this one done for a friend:
Pretty-well all of the Rivarossi heavyweights can be converted into wooden baggage cars, too. This one is the coach, re-done full-length, as a CNR express horse car:
Most of the other heavyweights (and the coach in some cases) need to be shortened if you want to make them into wooden baggage cars.
Don't overlook Athearn's "shorty" passenger cars, either, if you wish to make wooden baggage cars. They can be used as-is for many, or shortened further, if needs be.Here's a CNR baggage car, done using a photo of the prototype and technical information about it. The car was, I think, an Athearn Pullman:
Wayne
I've considered rebuilding some of my old Rivarossi/AHM HO passenger cars to represent cars they did not offer. I wonder what resources are available besides old MR and RMC plans that would offer a smattering of choices, I guess like the Locomotive Cyclopedia? No real goal for prototype(s), just want a little variety.
Mike