"THE MACHINE" was putting out a lot more than 340 HP, but the factory downgraded it (1) to give it an advantage in "stock" drag racing classes, and 2) for insurance purposes. While the engine block was visually and dimensionally identical to AMC's basic 390 on the outside, it was a special casting with extra internal webbing for durability, and most of the internal pieces were special high-performance parts. My father bought one new in 1970, and he shut down 427 Chevs and 440 Dodges with regularity. When he sold his MACHINE in 1974, the new owner got serious with it and cleaned up at the local dragstrip. It was a "loss leader" for American Motors, to get the word out that they were fully capable of competing in the horsepower wars. An AMC factory rep (very quietly) told my father, "You do realize that engine costs more than you paid for the car, right?"