Huh! Did not expect that would be the marque! Possibly but not that familiar with who was building Guercs in the early days to confirm or dispute.
I will dispute that the example linked that purports to be a "1969" build...nope, don't think so!
The Losa (yes, it clearly is) example is most likely "early '70s" as the seller claimed.
would love to hear from somebody who owns a legit "late 1970s" frame to chime in with a comparison