To find them, you'll need:
* Your van's year and engine type: The exact location will vary depending on the year of manufacture and the specific engine installed. This information is crucial.
* A repair manual: A service manual specific to your year and model Dodge 2500 will show you the exact locations of all the freeze plugs. This is the best way to find them.
* Careful inspection: Once you've located the engine and transmission, you'll need to look closely at the surfaces for round, slightly recessed metal plugs.
Without knowing the year and engine, I cannot give you precise locations. Attempting to locate freeze plugs without a repair manual is strongly discouraged. You risk damaging other engine components.