I am familiar with Dan's model and it is fantastic. I understand why he built only one. And I didn't mean to diminish any of the work he did on that model by making the point that the kitbash boiled down to removing the center bays. Obviously it was much more involved than that and he left no stone unturned.
I am not interested in doing that kind of a 99% kitbash because I want 40 of them. Instead the kitbash I'm talking about does
boil down to removing the center bay, adding a few details and living with a lot of things that aren't right. This is the type of kitbash I meant when I said it would be easy. I can't imagine many people would be willing to even attempt Dan's kitbash. Like you said, he only did it once.
My plan for a good enough kitbash is to 3D print some new parts, including an insert for the open area created by removing the center bay, new brake and door air equipment, and a set of interior braces. I'll have to ignore the lack of rivets and the embossed beads on the panels. I might not worry about the channels in place of the side stakes at the carbody ends, but I'll have to see about that. When I start with an MDC Roundhouse car, as in the case of the 10,000th Ortner car, I'll add the door opening hardware and do some additional work on the ends that the Athearn RTR version won't need.
Now if I wanted to build a model that was similarly faithful to the Southern version, I wouldn't kitbash it and I certainly wouldn't start with the MDC Roundhouse model. Instead, I'd draw it in 3D and break it down as a flat kit to 3D print. Then I'd have resin copies made of the individual parts.
I did something similar after I damaged my WrightTrak radio car, minus the resin casting part. I had already made drawings of the car back in the 90s before I was aware WrightTrak even existed. From those drawings I scratchbuilt a model from styrene many years ago. Later on I acquired one of the WrightTrak resin kits, but I damaged the body. So I went back to my old CAD drawings and modified them from 2D to 3D and then designed a kit, which I 3D printed. Here's how that turned out:https://pbase.com/mecrharris/image/167249896
But doing all that -- while certainly easier than Dan's involved kitbash process -- would cost a small fortune. A much smaller fortune can instead be spent fixing the things that matter to me: four bays instead of five, interior bracing details, adding door opening hardware, adding ladders at all four corners, etc. It won't be a perfect model, but again I need forty of them so I'm not aiming for perfection here.
Fort Worth, TX