I think you are right about the spindle length, but many cup/cone spindles feature an additional driveside offset of a millimeter or three.
If you bought a 118 or 120mm symmetric bottom bracket you could still add a cup spacer if the clearance was tight between chainring and chainstay.
I try pretty hard to reduce the chainline dimension using the shortest-possible bottom bracket (and by reducing the rear axle driveside spacing to it's permissible minimum), this allows fuller use of ratios while staying in the big ring.
On the bike pictured below, I remember using a much shorter bb spindle (118mm symmetric?) than the factory had installed (121mm plus offset?), and it works perfectly.
Reading through this thread, I will note that there were both swaged and one-piece versions of the 600 Arabesque cranksets, likely to meet different OEM-order price requirements. My SR Semi-Pro has the two-piece swaged variety but my Bianchi Super has the one-piece version. I believe the ones sold aftermarket in boxes were all one-piece for the US market at least.
