Welcome to the arena, and how about some pics?

I'm not familiar with frame size indicators on the limited number of models I'm familiar with.

The Cinelli Equipe Centurion had the 2-digit frame size stamped by itself on the bottom of the Cinelli BB shell.
The Dave Scott Ironman Carbon had a STxTT size formed into the bottom of the alloy BB lugs, even showing a 59.5 on one sized model.

I'm not familiar with models up until about 1983, and I know of none from there until Diamondback became the brand that carried frame size decals or stickers. I had a later-model Diamondback Expert that clearly stated 23" on the seat tube.