One other thing: I and another fella on his swap had the same problem. The ignition switch couldn't carry enough current in the 'Start' position to both hold open the fuel solenoid and crank the engine. He finally got his to work with another ignition switch. On mine I turn key to 'On' position to open fuel solenoid and have a separately wired 'Start' 50 amp pushbutton to crank starter over.
You can also mount another pushbutton under hood area for cranking engine from there instead of inside vehicle. That can be handy when bleeding fuel lines. This way, depending on how you wire fuel solenoid on ignition switch, you can either crank only, or crank and start from under hood when switch is on. Works for me.