Boy you're making it tough on an old guy , my memory isn't what it used to be when I owned a new 1973 Maxi van.
Hopefully your new ignition switch has the tumbler and keys , then you'll need to disconnect the battery and remove the dash gauge cluster .( 4 screws) pull the gauge panel out so you can reach behind to undo the speedo cable and electrical connectors one plug in and there should be two wires on the voltmeter that require a small wrench , mark those wires as to location .
You can then reach the back of the ignition switch to hold it while you turn the retaining nut on the front . Wiring on the switch is a plug in .
I'll see if I can track down a U tube video , on the Dodge , I know there out there for 70s Chevys , because without looking at the switch I can't remember how to remove the tumbler and key from the switch.