There is a fair chance, the engine is actually a Chevrolet. The Avant-Garde web site refers to the engine as a "383 Stroker", a phrase frequently used to describe a long-stroke small block Chevy.
Do you have a source of information about this car, which specifically mentions the engine being a Chrysler? We could know for sure by seeing a picture of the engine, but such an image does not seem to exist.