The first gravity car built in 1896 seemed an eclectic assembly, but by 1910, problems were worked out and the cars were standardized. Douglas fir was readily available then and was used for the structural lumber and decking. Oak was used for the seats and everything was painted for weather protection. Today's lumber is only stickered 30 to 90 days, and is mostly 5-6 grains per inch. In 1896, when these gravity cars were being built, Bessemer-process mild steel was readily available from the East by rail.
Chances are high that very little of any pre-Bessemer wrought iron was used.
Blacksmiths of those days did not seek the hardest way to build something to satisfy a purist's heart. Smiths incorporated each new tool and device that was invented into their shops to save time, money, and effort. One of my early teachers, Earl Burnside of Modesto, California, apprenticed in the Studebaker Wagon shop in Chicago from 1904 to 1908 and told me that they produced one wagon every five minutes on the assembly line, verifying the high level of expertise available at that time. By using ergonomic principals, I easily estimated the sizes of the gravity car's lumber, exposed nuts and bolts, benches, and brake handles. I determined the sizes of bearings, journal boxes, wood joinery, and the brake assembly by studying existing period-pieces in railway museums in California and Nevada, as well as at the Cable Car Museum in San Francisco.