Funaro & Camerlengo make a number of late 19th century rolling stock kits. They are not shake the box kits but fun to build once you get used to them. Accurail makes 40' wood fishbelly boxcars with vertical brake staffs. 36' was about the smallest standard boxcar once you got to the 1880's. Smaller boxcars were scrapped because of air brake requirements and they were too small to convert to air brakes and operate at a profit.