Novice question: I have mid-1980s Campy Victory or Triomphe 52-42T chainrings on my crank, and I'd like to swap the 42T for a 39T. I've done some cursory research on the subject, but am a bit confused about whether what I have is a "135mm" chainring or not. Or what. Put bluntly, I don't know anything about it at all.
I'm hoping that visual cues will help. Here are two views of my cranks:
1. The 42T in a single speed configuration, which is how it was when I bought it:
2. With the additional 52T ring (works fine with a modern Shimano 105 9-speed chain linked to a 9-speed Ultregra cassette, I might add).
Would the Salsa 135mm pattern chainring (see Lickbike page here) fit on my crank? Could I cruise eBay for any 135mm chainring, then?