I had some further discussion offlist and looked at some photos again, and I think you are correct. The early/mid 70's mod 99 does appear to narrow noticeably just a bit below the crank bolt holes, while the mod 93 tapers uniformly from top to the pedal hole. Thus the Mod 93 arm looks to be slightly wider, though not dramatically so. I need to actually pull out both cranks and compare side by side.
Regards,
Jerry Moos Big Spring, TX
Ken Wehrenberg <wnwires@htc.net> wrote: 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