I imported a couple straight-on side views into AutoCAD and prepared some window templates that I could print to size. I cut the templates out and glued them to the sides of the caboose with Elmer's glue.

Before I glued on the template, I removed the cast window frames and plugged all the side windows with 0.020" sheet styrene on the inner frame and another larger 0.020" sheet styrene plug cut to fit the outer frame flush with the exterior. This allows for a smooth interior and exterior and also allows for uniform cutting and drilling through the plugged windows and side walls.