My policy has a listed value for each crane, forklift, and vehicle (trucks) I own. I set the value. I also cross that list to my banker, so the #'s have to agree with each other, i.e. I can't tell the banker that I have a $100,000 crane and the insurance company that its only a $60,000 crane, to lower my premiums.
It might not be that way if you only have one truck and policy. And if its not listed as "extra" value, its not going to get paid to him, they don't care about all the extra fancy, unless you tell them and pay the extra premium.
Loss of revenue and the recent inframe paperwork are going to be his best route's, and if he has extra paperwork for the $ he spent making the truck fancy, that would help. I've found with ins. company's, the more paper you shove at the adjuster, the more $ he can justify giving you. If you can't generate paper for them, you're out of luck.
Do all offers in writing, nothing said over the phone matters.