As built the boxcars had needle beams that were too close together to allow a combined K system to be installed. That is why they utilized the split system as built. When the cars were rebuilt, the needle beams were moved farther apart which allowed the combined K system to be installed. As mentioned it is still a tight fit. An oversized hole in the needle beam is required to let the brake cylinder piston to extend.
I always thought it was interesting that the C&S invested in new cars, and kept their original small locomotives, while the bankrupt D&RG(W) rebuilt their own wood cars, upgraded the track and bought new, much heavier locomotives. We can see whose railroad lasted the longest.......