Your might want to look at sites like RR Picture Archive or Railcar Photos. Lots of 70’s to current freight car photos with dates when they were taken. The Canadian Freight Railcar Gallery is also good.
The “Northern New England Color Guide” is pretty much a pure picture book, in color, with the date of the photographs in the captions. It’s my go-to source for rolling stock projects. I’m pretty sure they did other books for other places.