ORER for May 1903 shows CB&Q 42138 to be a furniture car with an inside
length of 50'3-5/16", so the camera isn't fooling us.

As for the MP cars, they definately are not cabooses as the same source shows
MP cabooses at that time to be numbered 1-187. The only car with a legible
number in the picture appears to be 2610. However, in those days it was
common practice to use cars in MW service without a change in
number...numbers were reserved mostly for cars bought or built new for
nonrevenue service, and cars taken from freight or passenger were not then
renumbered. Sometimes they weren't even altered, and there are numerous
pictures showing large gangs of men standing in front of revenue boxcars that
are obviously being lived in.