When I built #10, one of the innovative and useful ideas was to create both running boards out of a single large piece of brass. This helped me get the boiler level relative to the running boards, and since Pembroke is not an incline railway, a level boiler is desirable.
I’ve planned the same approach with the virtual model of #622. Interestingly, using the Finish Sheet Metal Model feature, you can include the parts that tie the running boards together in the etch plan, but exclude them from the finished parts.
Here is the finished state of the workbench. By finishing the model, I could extrude away the tabs that hold the running boards together. However, they are still in the flat pattern as shown by the blue arrows.
Here are the steps. Ignore the flange and the move face.