lower control arm clearance

I'm just going from memory and not even on my own car. My friend got a similar set up for his Dart. His car sees no street use at all.

I personally would not drill out the taper. It's there to make a tight press fit to the steering arm so there is no play in the joint. The stud is in shear so all the side to side pressure from turning the steering would quickly wear a straight bolt or the hole in the steering arm, whichever is softer.

As far as a wheel spacer, you'd need a pretty thick one. Remember, the tire's going to flex when you turn so you would need to have extra clearance.

Sorry, but your best bet would be going back to the factory suspension for the street.