NightHawk,
Welcome to CHR! From your post it's pretty clear that you understand very well how to read the part number segments (even though you called it a "serial number by mistake), as spelled out in the post above. Unfortunately, the meaning of that "T" ending character is illusive!

Hopefully one of the guys here will have something from some old 1970 info that spells it out for you. Glad to have you here.