Next time you pick up a older bike look at it closely.

Theses things wont hold true to everything but it will help.

Look for RD that are attached to to a rear dropouts instead of it hanging off the rear axle.

Shifters attached to the downtube rather than attached to the stem by a clamp of some sort.

A crank that can disassembled, aka not a cottered crank.

The first bike that I began riding distance on was a 79 peugeot UO8.

I found it at a used place and it required a little fixing but it definitely stood out from the other 5-7sp road bikes.

Oh word of advice, older french bikes the BB threading headset threading are almost obsolete. Or the parts are hard to find.