8 3/4 whats it fit?

The track is the center to center distance of the factory mounted wheels. If your wheels are a different offset from the factory, then the track changes. The factory rims IIRC were a zero offset wheel, thus making the track equal to the drum to drum measurement.
And as was said, only A-bodies ever had a 43 inch perch CC


EDIT;But if the factory wheels were a 1 inch positive offset, then the track would be 2 inches less than the drum to drum measurement.Similarly, if the wheels were 1 inch negative offset, then the track would be 2 inches more than the D to D. So bottom line is this; without knowing the oem wheel offset, the track width measurement is useless.