Jerry opined: I could be wrong, but I didn't think there was any difference between a mod 93 and a mod 99 left arm, provided we are talking about mid-70's or earlier.
I think that there was a difference in that the cross-sectional shape of the 99 crank was more square than the 93 which was more rectangular, with the long axis antero-posterior. Thus, the 93 had more material in the arm as well. The early 99s had a polished finish which, as time went on, was in my mind, less well finished.
Ken Wehrenberg, Hermann, MO