When you change or adjust the upper control arm all you are doing is moving the spindle to the specs you want so if you can move the lower portion of the spindle forward would that not help with more caster?
When you're adjusting the upper control arm you're just tipping the spindle at a different angle, you're not significantly changing the location of the wheels. If you drill the spindle to move it back a 1/4" with respect to the lower ball joint you're changing the wheel base of the car. Not to mention the caster, and drilling the spindle so it slides backward to gain tire clearance at the front corner would make the caster more negative, which is exactly the opposite of what you want. These cars already can't get enough positive caster with the factory control arms and bushings.
The spindles are symmetric. The issue with the tire clearance is because of something else that changed when the spindles were swapped.