Using mustang rotors for 4.5" bc

are you measuring BS to the inside edge of rim or the tire bead? I had some 4inch BS wheels I tested, and there was more than 1/2 space left to upper balljoint. I also had some 5in BS wheels, and they definitely hit the upper balljoint when you tightened it down. That was just a test.

Checking BS from flange to inside end of wheel.