They are terrible. You don't want it, I'll take it off your hands and do you a favor.
Honestly though, it seems anything with a diesel has increased in value the past few years... consider it a hipster tax- hipsters who don't know dick about cars want old diesels to run on vegetable oil. It's the cool thing to do, apparently.
Is this a 620 or a newer truck?
Value is really going to be on a sale-by-sale basis, I don't think enough of them change hands frequently enough to base a real value on. Bluebook is complete BS for absolutely anything more than a handful of years old anyhow, regardless of collectable status or not. A car that old has far too many variables to be taken into play regarding its value.
It scares the bejesus out of me that someone, somewhere ordered the Lusitania with front drum brakes.