71 sounds about right-- Columbia made these in the 1960s-70s era.

They're not worth much but are very reliable and tough. The overall quality had slipped a little since the 1950s era at Columbia, but these work fine usually, even after 40s years. They're easy to service and fix, and should use 24 tpi threading rather than the Schwinn 28 tpi. I suggest a basic clean up and I would get a new set of caliper brake pads. You can still find fitting pads at your local bike shop probably.

A Brooks probably would be overkill, considering its overall value and cost. What you could do is find one of those black vinyl mattress saddles with springs though. They used them on some of the English bicycles, they look nice enough, and would add a little spring for low money to that bike.