^ Know what you mean. When I bough my '85 Mondiale I measured it three times while talking to the guy and was certain since it was 57.5ish it would be fine despite my preference for 59. The difference was immediately noticed, however only after a full rebuild with a completely group.
I still say keep both, or shop the original as is.
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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