Tichy USRA clone kit
The drawings do show a Viking Corrugated roof, but I've never seen any photos of it on any N&W car. I'd recommend sticking with the Climax radial roof.
Another tricky aspect of the class BL and its rebuilds is that the diagonals are not parallel. The outermost pairs match the standard USRA plan, the intermediate pairs are slightly more vertical, and the innermost pair are slightly more horizontal. This is because the half door is wider than the spacing between the vertical posts on the USRA design, so the middle vertical post was moved toward the ends. This is shown most readily by the SK stock cars after they were rebuilt with Z-bars in the early 1950s: