This HO Scale cupola is designed for Canadian National's modernized snowplows. Originally built with a flat front, CN added the sloping front window section to reduce snow buildup while plowing.
This cupola reflects the actual dimensions of the cupola.
A second version is available which will be narrowed to fit the Walthers Russell plow, which some modellers are using as the basis of a kitbashing project to represent the CN plows: https://www.shapeways.com/product/DWBE83KGR/cupola-slope-front-narrow-for-walthers-plow-cnr-ho?key=795e40e17fdd4046d91a5d17ace460c3 .
Available in both FUD and FXD.