I worked at Monroe Truck Equipment for a few years while they were building over 100 trucks for one of the train railway companies. Every truck had a crew cab conversion and a frame extension. All of those trucks were done with the process I outlined, They also built tandem dump trucks with center blade snowplows for many states, as well as several fire trucks. The outline I wrote was their standard procedure but that was several years ago. Things may be different these days, again. Gene