I Chose the 383 Big Block

I'd try to find a duster & year specific wiring harness, rather than a universal type harness. Do some internet searching or contact slantsixdan (User name). He sold me a new wiring harness to run halogen bulbs that was spot on, and answered numerous questions I had when installing. If he can't make you a factory style harness, he can probably refer you to a good source.
@slantsixdan can you please help @TommieDuster76 ?