As for the roof and the bays...more than just new holes. Depending what style gives us the best range, a new pattern would be appropriate. If I were to need new openings, I could do it with an arbor press or one of the CNC Mills. We have some body styles that require secondary machining to remove details for specific roads.
Welllll then... Joe, please consider the WP's cars. The ICC-built later cabooses have the same roof as the SP car and even the WP historical society mentioned the new MT cars as being an almost dead ringer for them. It was a small run but they're blank on one side, with a smallish curved corner window on the other.
But the 426-460 series, 1955 era ICC cars, is what I really need. I hope you'll consider a new roof (diagonal panel) and bay (sloped roof) to match those. I suppose I could cut the three windows myself if need be.
Have you considered offering different window castings so those who want proto-specific can do so on their own? (I know, 'Do it on their own?')
BTW, what's the build or service date on that new PC boxcar?