The catalog gives no reference to it. I would think it had something to with the gearing, maybe there was change the Nuovo Record RD that year that it could could handle a 29t cog?
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk