Richard,

It's like any other car situation. There's more to value than the car name, and a partial description of the engine.

Which model Plymouth is it? How many doors? What kind of equipment? What makes the 440 special? This question because Mother Mopar never used that designation, so what does it really mean? Is it a numbers matching car, or is the 440 a transplant? Which trans? Any modifications, e.g. fuel cell, roll bars, any other boy racer silliness? Are you asking because you want to buy it, or is this just to check if he's letting his mocking bird mouth overload his humming bird butt?