Gas to Diesel Engine swap?

Is that even possible? I would love to get a nice big conversion van for long trips. However, they are just about all gasoline, even cargo vans are mostly gas. Diesel fuel is much more effecient and cheaper, here at least. Is it possible to buy a gas conversion van and then engine swap with a diesel engine. If it is possible how much $ might it cost and where would I go to get it done? Thanks

Anything is possible. It will probably cost a few thousand.
Some of the changes I can invision are, but not limited to
wiring changes in the dash and engine compartment
complete fuel system from tank to motor
don't know if the current transmission is compatible with the diesel motor
exhaust system
engine and the assorted accessories (manifolds, air intake, etc.)