Not as a business, or other, still working on more for myself.
Here's what you do.
Using a straight chisel knife, carefully cut off the grill rivet details and headlights. Using model putty, fill the grill and headlight areas and sand using 600 (or finer) grit WET sandpaper. This will take multiple efforts to get smooth.
Using evergreen tubing, new headlight housings must be made. Note the all the early housings were NOT the same size. Drill and cut for new housings - CAREFULLY. Will probably need some putty touchup work afterwards.
Detail as desired. Be familiar with what you are wanting to model as details and accessories varied greatly.
Note I start with the CN version as there is less lettering to feather off for a paint basis.
Also note the if you add ERR TMCC control, change the sound to ERR sound (must do to work properly), add electrocouplers, and change the headlights. by the time you add in a core you will have well over the amount of a Lionel or MTH Medium to large sized diesel. Then you have painting costs as well.
Was hoping MTH would do one with DCS, but that aint gonna happen now. But if you want a 3 rail 70 tonner this is the only game in town.
That's it in a nutshell, all I can say is Jump in and swim, that's what I did. I've done probably 2 dozen for myself (not all with the electrical upgrades).