The info you are seeking can be as varied as the number of prototype railroads to be found in the universe. For example, if you model the Pennsylvania Railroad, I would start by joining the PRR Technical & Historical Society and then acquiring back issues of their quarterly magazines. Current issues will be free with membership.
You can also search the net using terms like "PRR boxcars" and "PRR locomotives." You will find that most, if not all, PRR equipment is given a "class" designation. For example, steam locomotives with a 4-4-2 wheel arrangement are "E" classes ranging from E1 to E6, I believe, on the PRR. Other railroads using the same steam wheel arrangement freely used different classifications.
Diesels are a different story. In PRR's case, all of these classes were assigned by the railroad so that diesel classes rarely, if ever, matched the manufacturers classification. For example, a PRR owned EMD F3 (manufacturer's designation) was actually class EF15 in the PRR books. I believe most other railroads just used the manufacturer's classification.
In this historic search, you will find that some PRR equipment was provided by third-party vendors (Baldwin, ALCO, Pullman, etc.) and some was actually manufactured in-house. If in-house, PRR will be your actual manufacturer and the PRR's class will be the equipment's designation. For third-party manufacturer's, you may have to search their records once you find out who they were from the Pennsy records.
Finally, just so you know, the data on most O gauge car sides is not accurate and may not even represent a real car number that the prototype even used for that type of car. So the question you must answer for yourself is: Do you want your database to include model data, authentic data, or some mix of the two? And with respect to trucks, just search railroad rolling stock trucks for info. You might even specify freight, passenger and caboose trucks if you so choose.
Chuck
