7 1/4 Vs 8 1/4

Is the seller talking axle flange or backing plate flange? A lot of 7 1/4" rears were wider for cars that originally had 9" brakes. 10" brake 7 1/4" rears and all 8 1/4" rears should be the same.

I seem to remember the Mopar Chassis book explaining this in some detail. I don't have a copy handy, but perhaps somebody who does can post the facts.