1976 Plymouth Feather Duster

Locomotion said

Don't have time to look up the articles at work, but I guarantee that V-8's were not an option from the factory. Feather Duster and Dart Lite were a complete, optional package with special tuned /6, auto or 4 speed O.D. stick, special gearing & aluminum bracing under the hood, trunk & behind the bumpers.

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That agrees with the dealer data book
The 1970 Hamtramck Registry - 1976 Plymouth Dealership Data Book - Valiant/Duster

That's someone's hot rod project. A collection of parts which may or may not add up to a good package.
Execution looks like there will be things to figured out and fixed. Expect it will need to be tuned and hot rod tuning is a project, not the same as a tune up.
Wiring has been hacked. '76 has some unique wiring. If, or rather when, there are problems troubleshooting and fixing will be more difficult because of the hacks.