Well, I thought I had researched this pretty well before buying the large nut for my '73...think the final word for me was found here at cc.c... Tonight I see, not that they are the final word or anything, PGclassics sells both nuts..same price...small nut listed as 70 e-body, large nut 71+b-body...on the mirror set for 71+ e-body they include a large nut, on the 70 mirror set no nut included....
Soooooooo I suppose it's clear as MUD now.