Front Rubbing - Tires, Suspension or Wheels?

That program would have saved me a little time. I have a sketch pad sitting here at my desk with almost identical diagrams drawn out.

I'm pretty sure my rear axle isn't a factory 8.75, but its pretty close. I guess the only thing I'm concerned with at this point is will a 275 still allow me to lower the vehicle (more than it is now)?

This is my first car where the axle and wheels/tires came from:



I'd like for it to sit just a little lower than that in the rear. Lower than mosleyme's car in the above pictures (mine has Mopar competition springs that I'd like to swap out).

Thank you both for your help. I've spent way more time on this subject that I cared to, but I only want to spend $2k one time.