I'm not an expert, but wouldn't one of those small sensors mounted in the area just above the intercooler that would detect heat or fire be useful in this application? Thinking about the type of sensor that they use for burners that are supposed to light and if they don't the sensor doesn't get tripped it shuts off the fuel to the furnace? It could be tied into the ignition circuit or the fuel delivery circuit if your using electric fuel pumps.

PS-Gerry, got one 540 done with your heads, runs nice, thanks.

Perry