[SS Tim]

Interesting thought on the "T" and "S" being A/C option status. That may very well be so. But I don't agree that in this case the far right set is something other than "Z84" (CST RPO#). This three character group is a common run and size with the next character "T" being a larger size and at a greater angle relative to level. The "T" is however very similar to the model number that follows is a progressive downhill run. To me this indicates the markings were written as seperate, distinct groups. If you have other clear examples of a "4T" grouping in this location without the CST option or other potential option number overlap I'd like to see it. At this point it would appear that "T" alone could indicate A/C, especially as it is repeated on both ends of the firewall.