The Univega....but that's no 21" frame. Looks to be 57cm frame.

Cannondale and Trek are out, vertical dropouts.

Miyata Pro....small frame....50-52cm. And top line racing bike, not one I'd make a banger. Too good.

Miyata 112 is likely a good choice, lower end, decent quality, cheaper.....but no pics though.

I was going to advise a lower end Japanese, a Giant, or Peugeot from the mid 80s.
Later Peugeots should have the French threading or sizing issues. I believe they went to ISO.
And they ride like a dream like most French bikes.