1988 Dodge Diplomat with 318 gas AND propane hybrid?

Is there such a thing? The car is an old Sheriff's car from Herman, NE. If there is such a thing, how do I get the propane part of it working again? It has a small tank/pump combo with the markings stating that it should contain propain on the engine but the pulley is siezed. Runs ok w/o it. Any suggestions?