Yes you are wrong. And yes you need a wider range of hands on experience because your thinking is limited. And no my body work is all stock.
Let's just say that what I've written is a good bit more limited than my understanding and leave it at that.
Lets start at the top with your strut hole. Make it bigger. Buy some good camber plates. Max out the camber.
The big strut hole isn't the limiting factor. Just why, I don't know, but FWIW the car's as-delivered camber settings were right around -1.7° against Ford's -1.5° max-negative number. I have Steeda's HD strut mounts, which claim ±1° camber adjustability. But I've only been able to get to -2.0°, just barely. There is spring to tower clearance (OE-style springs), maybe as much as half an inch, but something is making for a hard limit against further camber adjustment. Not that -2° is a terrible place for a true dual-purpose car (and perhaps more representative of the average 90% street 10% HPDE car even though that's way too mild for hardcore competition).
Now for the strut, slot the holes and/or get camber bolts.
If I was getting full adjustment at the mounts, slotting the holes (or simply drilling new ones) would make sense. I've done this exact mod before on at least one other car, but it's not worth doing on the Mustang until I can find out why I can't get past -2.0° as it is. I did slot the hole where I could pry against the mount's little pointy tab.
For me at least, aftermarket camber bolts/crash bolts are a non-starter. Keep in mind that my '08 came with the early coarse-thread strut to knuckle fasteners and the early knuckle design. The arrangement that produced a number of knuckle failures in autocross and track driving that was traced back to insufficient clamp load, that in turn called for stronger fasteners (which I now have) and a knuckle design having a slightly thicker (0.020"?) strut mounting pad thickness. But once again, I've addressed camber adjustability at the knuckle before as well, so I'm familiar with what's going on.
Adjust it such that you are back to your original camber. Now you will have about 1/2" of additional strut clearance. Buy wheels with an addtional 1/2" offset. Buy 305 tires. Take new pics and call it good.
Don't forget that the poke I'm getting is with -2° camber already. Not Ford's preferred setting of -0.75°, or even their -1.5° max-negative.
If I can somehow get another half inch at the strut mount, that's only about half an inch at the tire, which would put it pretty darn close to flush. I'd have more negative camber (roughly another whole degree) but as that only puts the tires flush there isn't any room to dial camber back down to -2° at the knuckle (if dialing it that far back was what I wanted to do) without pushing the tires back out past the fenders.
I suppose it's possible that a coilover setup would make this all easier, except that I don't think that good coilovers in year-round street duty in the Northeast is a particularly good idea. Cheap coilovers be an even worse one.
Norm