Nice to see the Argos back on the road! Thanks for the update. Classic campy drivetrain -- as it should be.

This was the weight weenie era after all, and it is possible that it was made from some extra light gauge tubes and in fact should have a 27.4 post. Sounds like a question for T-mar. The only real way to tell for sure is to test with a 27.4 seatpost, or a real seat post sizing gauge thing.