The boiler jacket is a thin shell (No. 20 sheet metal) that wraps around the boiler. There is a space between the boiler and the jacket for insulation.
Originally, the CK Holliday had a dark gray boiler jacket, so I tried to duplicate it here:
The brass bands are usually secured at the bottom by a screw or a bolt to tighten the band against the jacket. Except for where the bands terminate at the firebox. I’m not sure how they are secured in that case.
The engine underwent a lot of changes since 1955. One of them being the boiler jacket getting cut short. Instead of wrapping the boiler entirely, the jacket terminates somewhere under the running board. Here’s the jacket as seen at the Fullerton RR Day:
Another change is the running board. Originally the CK Holliday had tapered, split type. Today, for ease of fabrication, the board has been changed to a straight type. Compare between 1955 and today:
Of course, the model will have the original running board: