This is an HO scale cab and boiler for Savannah & Atlanta #750, based on drawings of an FEC Pacific. No running boards or cab base are provided, however holes for 1/32" or .032" wire are provided in the boiler, to serve as running board supports. Where the holes do not co completely through, there are indentations inside to assist you in getting the support rods installed straight and level. I recommend building the running boards out of .030" brass or styrene, to the dimensions shown. The smokebox has provision for a 1/8" (as used on 2-56 threads) hex nut for mounting.
Note that this product was designed to be printed in Frosted Ultra Detail, and some of the walls are quite thin. I am offering it in Frosted Detail because of the price, but I cannot guarantee that it will print properly. Order it at your own risk!
Note also that this model is based on drawings and photographs of the prototype, and is not expressly designed to fit any commercial chassis. You will have to modify or build a mechanism to fit, and probably modify the 3D printed model suitably as well.
I have a wooden cab version available also: https://www.shapeways.com/model/2943447/