Go to mafca.com, click on "references" in the left hand column, then click on "data". The first subject in the data list is the study by Dave Sturges about assembly plants and their corresponding letter codes on the frame cross-member.
THANKS to Michael in Sedona where I wish I lived and Mike V. in Florida where I enjoy visiting, for the information on codes of build locations.
Joe Grobleski
Cape Cod