What are the codes on the buck tag?
EXT = ? Exterior Decor Group??
PB = power disc brakes
RM = rocker moldings or race mirrors?
Coding can get confusing since it differed from year to year and plant to plant - even changed during the year according to the manager I talked to about the coding. He was the guy that choose the codes and issued the changes/updates
According to Kevin Marti's The Mustang and Cougar Tagbook research (if you have the book you'll notice some of the members here are listed in the "credits"
RM = Rocker moldings (the "Race Mirrors" used RAC
EXT = Exterior Decor Trim
PB = Power Brakes - though at the moment not sure what change to the body was necessary for that option
Will look to see if I can find anything on the one remaining part of the original question