I just received a 1985 Trek 400 frameset today, with the cool investment cast lugs. The serial # is 18346x, with a serialization date of 2/25/1985, from the list at vintage trek. Anyways, I pulled the cable guide from the BB shell, for cleaning purposes, and found an upper case letter "R" stamped into the shell. Is it safe to say that would be a maker's mark? And if so, any idea who that was? Obviously, it's not really important, but curiosity demanded that I ask. Thanks for your time & knowledge.