I bet the rear dropout drive side does not have the bosses forged in for the chain rest, if so, my guess, '76-78.
The headlugs look un thinned and if memory serves British in origin? Maybe French.
A lug look I associate with MKM, or Bob Jackson by this era.
The head angle may also be a bit shallow, indicating a use as found, no blacksmithing.
Rebuilt front end.