I’m not mechanically inclined enough to be able to do all that you just said.
You gotta pay to play. You can push to the edge of what's possible either with $$$ to have someone else do the verification for you, or with your own time/effort, or with $$$$ for new tires+tow+possible further damage repair. Take your pick.I’m not in a position to try different spacers out, so I need to make sure to order the correct one on my first try.
I can fit 305s on +32 offset wheels in the rear on OEM P rotors, so, pretty much the equivalent of +35 wheels on non-P brakes. I probably have 1.5-2.0 degrees of camber more than stock in the rear, which is very roughly equivalent to 15ish mm of extra fender clearance. Which means that 275-wide tires would probably be okay with stock rear camber. With your 265-wide tires, and +30 wheel you're already at the same fender clearance. Now, I left a safety margin, so a 5mm spacer would probably still fit if you don't plan on cornering hard.