Replacing Ignition Switch in 73 Duster

I can fix or even diagnose all of them from here. :(
After reading the history of your troubles here's what I guess,
In removing heater core you created the fuse blowing problem.
In replacing the relay and /or that battery cable, you now have wire terminals touching one another which would cause constant crank.
Strictly guess work though. All I got left for you is my best wishes