Both 69 M code 440 ’Cuda, and the 68 426 superstock prepped by Hurst were legendary. Can’t forget the Plymouth Savage GT modified by Auto Craft in Milwaukee, available w/ a 340, 383, or 440, fiberglass deck lid, roll bar, Lake side pipes, unique grill inset amongst other rare goodies. Very few built even less survived. There are a few web sites out there, and a Savage Registry for those interested.
The 66 barracuda could be had with a solid lifter cam, that was a more aggressive profile, holly carb, special intake and tubular headers, rated at 275 HP. Not bad for 66. 1Hp per cube in a fairly light car.