Your pretty funny.
Obviously you started correctly, open a beer and drink it first.
This will be very similar to what you've already done on the inner fender panel, you're just removing less than the whole panel. Think of how you pulled that panel off already, then think of just going halvsies on it. That's all you're doing. Easy peasy, really. You are just removing the outer skin of the a-pillar.
Do practice with the donor. This will give you confidence on your car. Cut just as deep as you need to get through the outer panel where the panels meet together. It's not that hard, really! You'll see. And so what if you need to go down to the rocker?
Which brings up a point. cut the donor car panel quite a bit larger than you'll need for your car. It's easier to trim off excess than to add back more.