Problem Starting Up

74 Dodge Dart Swinger Slant 6 This is my problem starts up once w/key no problems, I'll have the engine on idle for up to an hour, turn it off, then it won't start up again. Put in new control box, ballast resistor, starter relay, coil, cap rotor, spark plugs, starter, battery, neutral safety switch. Please help on what you think I could do! Going crazy!!!!