[mechanickeith]

Shutting off the ignition/mag at WOT does nothing!! By that time the spark plug is lit like a welding rod & it will continue to run. After a good hard pass, the ground electrode will be totally burned off down to the base of the plug. Plugs are good for 1 pass only. Shutting off the fuel is about the only way but it has its consequences, You shut off fuel at WOT,, the motor goes lean, gets super hot & can melt the heads right off the block.

Back in my old Detroit Diesel days, had a 6V53T run away, was very lucky that it still had an operational emergency shut off flapper on the blower intake. Pulled the emergency handle & it shut right off. Big spring loaded door inside of the intake that shuts off the incoming air.