You most likely have a F163 continental engine in this truck. Check to see if you have a vacum switch on the intake manifold above the carb. It needs vacum to work and turn on the LP lockoff switch. Also some of them had a oil pressure switch hooked up through the starter circut. As long as you have oil in the engine and good pressure when cranking it would turn on the LP lockoff switch. In any case check to see if the lockoff valve is getting 12v? Also you can take the lockoff valve apart. remove the coil then the center plunger assembly. Check the little spring on the end of the plunger. It gets loaded with rust from the tank and the spring won't compress to let the fuel in. But like I said you need good cranking vacum to start. If it has a Impco carb on it? You want to check it out too! If the engine is beat you may not have enough vacum as needed. You may want to also take a compression test. Goods about 140 to 150 lbs. Take care ETS.