“I see a series of at least 5 rings where the car side meets the roof. What are they?”
Lifting rings to which chain blocks were attached for lifting automobiles or light trucks for tilting or decking prior to the more common use of Evans or NYC auto racks. This is definitely a 40’ auto car with staggered doors.
“I also see something at the peak of the end (a rectangular plate with maybe a chain dangling from it?). What is that?”
I see it and agree it’s very small chain or a stretch of rope, but am unsure of its purpose.
“Finally, in my ignorance, I am surprised that the lining of the car side does not go all the way to the floor. Are boxcars commonly built this way?”
Commonly referred to as “belt rails” and another staple of auto cars from the ‘teens, 1920s and 1930s. Heavy boards for securing blocking, bracing and temporary decking.