Well, there are a couple numbers you'll get based on the type of Dodge guy.
What you have is a Cummins 3500 Dually with a 5speed manual, running some strange propane fuel system. It has an aftermarket clutch and driveshaft.
The real talking points are dually, Cummins (downside, it runs propane) Manual trans. Everything else is a throwaway item, clutches are a maintenance item, the only use in listing it is if its new and won't need to be replaced for awhile, its like tires or sparkplugs on a gasser. Propane is a downside simply because its not a known quantity, it requires even more specialised technicians to work on it (I am a diesel tech by education, there are so few of us in the auto market its hard to find a decent shop with decent prices) than the already scarce diesel techs. Since its propane, it's more difficult, even if only slightly, to find places to refuel, especially to the uninitiated.
To a Dodge guy who wants a 2nd Gen and is willing to spend money on it, a fair SELLING price is somewhere around 8K, at least in my area as long as the body has little to no rust. If it were a stock 12V you could reasonably get 10-11K from it. To the right person, if propane is a requirement you could get 13-16K from it, but thats a one in ten thousand find.
To someone like me, who is a Die-Hard 2nd Gen Ram enthusiast, i've spent more than 5 times what my truck is worth just to keep my baby alive and well. I wouldn't pay more than 5K for this truck if the body has standard Michigan rust, if it were pristine, I might go as high as 7K, but not much more. If I bought it, and you took it back to running diesel before I bought it, i'd pay no more than 10K if the body were pristine, Every door or fender i'd have to replace drops the price from anywhere from 500-1K each.
Trade-ins to dealers is just gonna be a joke.