I recently acquired two southern tuxedo painted FTA's without rd numbers, searching thru some archives I found about three or four different number series I can use on these. Some were A&EC, cnotp, and ags, but no picture I have found of the real units shows sub lettering which I would like to use, I can make out something in these pictures near the rear of the units that I guess could be what I'm looking for but the image quality won't let me be sure of it. Did they actually sub letter these in those days? If so where at on the car body?