Boxcars with walkways will be used for the mid-60's era operating schemes.  These will receive details like separate grab irons, thin profile walkways, and uncoupling levers, but most will keep their existing paint schemes.  While this might not be particularly prototypical, it adds color and variety to the layout.

 

Boxcars without walkways will be used for the mid-80's era operating schemes.  These will also receive details like separate grab irons and uncoupling levers.  Several of these that I have are Kadee cars from the '80s, which are colored plastic with lettering (as opposed to being painted) which looks out of place to me.  So, I will repaint those when they get detailed, and those will probably be lettered for some of the fictitious roads.