Factory wheels on these older cars generally needed to run close to a zero offset, +/- as much as 1/2". Excessive offset could cause wheel bearings to wear prematurely.
The drum and disc brakes' hubs sat about 1/2" or more different relative to the spindle. Drum cars generally only ran a 6" wide rim.
Wheel face design determines caliper fitment, which has nothing to do with backspace or offset. If you determine what backspace you need by measuring your car, that is the backspace you want, regardless of which wheel design you need. Not all RallyIIs will fit the early 4piston brakes because of the shape of the wheel face, not because of their backspace.
I currently am running two different width 15" rally IIs. I think front is 7" and the back is 7.5", but not sure. I'll check at the next balance. I believe their backspacing is very similar, and may be between 4-4.5"
