We quibble occasionally about use of the term 'classic'. My opinion would say anything produced by Antonio Mondonico is a classic, even if he doesn't get the recognition of some brands. I met the man (very briefly) in the late 80s at a shop in Santa Clara (or was it San Jose). He was taking measurements for custom builds, and I wasn't buying. The Thron tubing is a mid-level tubeset, giving a compliant ride. Thron chainstays&seatstays were often used by some builders when the main triangle was exceptionally stiff (by the standards of the day). I think a 1990s era tubeset with some carryover into the 2000s.

I had a Marin road bike (Billato built) with shaped Brain tubing in 1999. I wished I had bought the next model down in the line-up with Thron tubing.