Yes they are modified all the time but just because they are does not make it right and safe. If the manufacturer is out of business then I would not want to make any modification but purchase the correct truck or equipment for the application. I would not want to have a second party document the modifications what happens if they go out of business? It is all about liability and do you really want to put yourself in that position? One issue like this and you suddenly no longer have a business. Some times it is better to walk away from a situation and maybe loose a small customer like this than loose everything your or your employer has worked for.