Look for a bike boom era Atala frame I have two. Horiz. dropouts, sweet chrome lugs, and cheap-ish non- butted tubing so they're not very coveted as vintage frames go-- but they're not boat anchors.
And I believe they're 70x70! I grew up riding them, built one up for my father (I got his stolen back in the day), and still have my mother's to restore and build up by the time my son can fit on it.
Did an MS150 on one when I was 12. Smoooooth riding bikes.