How do you mount a bag that drapes over the sides of the wheel with clearance that’s *too narrow* for a modern pannier rack? Racks are too wide for this vintage swiss military medic’s bike bag, as they’re ~3 inches wide and the width of this bag’s channel is ~1.5 inches. What did they use back then?

This got me curious. After doing some searching, I’d say the Tortec Velocity rack might be your best bet, as it’s narrow and tapered: https://www.altura.eu/products/velocity-hybrid-rear-rack

It’s 65mm wide at its top platform, then tapers out. Not sure on shipping/availability if you’re in the U.S., though.

FWIW, using this bag on your bike is against the Geneva convention (unless you are a medic in a war zone).