Rees pretty much played on the right side of a back three. Mully is a right back. Hard to compare.Siggy can play left back...
I don't quite get this, so will appreciate your educational reply, because back in my day (no pun intended!, and don't ask how long ago it was!!!) a right back was on the right at the back.
His job was to stop and/or to contain the left winger, or whoever else had the gumption to get down that side of the field.
Back three formations tend to rely on three centrebacks, rather than one centreback, a LB and a RB. Rees was a CB. He was the rightmost of the three CB's, but that doesn't automatically make him an RB.