On a big, low-compression engine like the 426, about all that a spark plug needs to do is light the fire. As long as the thread diameter and length is correct, there should be a wide range of plugs that will work, especially if you're not planning to do a lot of hard pulling at max RPM and wide open throttle like these engines were designed to do. As long as the plugs don't foul out from being too "cold" of a heat range, you should be good to go.
Jerry
