Have you considered handle bar mounts? I actually have much better pics but can't find them.
This is a Minoura cage mount that use two U bolts to attach to the bars and I put a double bottle attachment I got of the amazon. For some reason my '90 Bianchi Proto only came with one set. For a few years I a set of nylong Zefla band type mount but it left marks on the paint. This set up allows to carry two bottle or if I want a bottle and this GU can with my spare tube and levers
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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