Now that I have half a dozen S-S frames under one roof I've been able to study some differences. 34 to 36 appear to have no differences. 37 is one-year only. 38-39 are very similar. 40 to 42 are very similar. 640-B (not present, but literature says is strictly a military sport scout, just green.
741 gives me a few head scratches. The tank mount holes are further apart in front. Is this an odd-ball frame? Or did they use a taller neck to go with the lengthened forks? and maybe use Chief tanks?
any answers welcome, corrections, whatever.