bossman, many thanks for the offer. Great idea, but it looks like the ring sizes posted on your local craigslist are not what I need (and then there's the motley collection of damaged and orphan crank arms ...). My TA rings are 28/40/49; I just got a 34 inner to replace the 28 (overpaid $37, would have loved to get your local 33 for $16 OBO); now looking for a 52 or 53 outer.

Hoping at the end of the day it will all shift properly without also replacing the front derailleur. It's the original Suntour Cyclone from 1977, a double derailleur over a triple crankset. It was unable to upshift from the 28 to the 40. The 28 was only an "emergency gear" for hard climbs that you had to get out of by stopping and manually lifting the chain. I'm hoping it will shift fully between 34/40/52 or 53.

TA rings are available here and there, just not usually cheap ...