Oh boy, the pressure!
Sadly, I must disappoint. As
@juvela mentioned, this is indeed going to be a needle-in-a-haystack kind of a thing. Everyone and their
mamma used these lugs back in the day. Finding who made this particular frame will be tough.
Looking at the stay ends made me think
Gloria but then I think they stamped their numbers on the back of the seat lug (plus were normally 6 digits?).
I'd say the most common placement of frame numbers during this period was on the seat lug (back or side) and seat tube. Of the brands mentioned earlier, Olmo I think also stamped side and back of the seat lug, and had a format that started with a letter followed by 3-4 numbers.
The pointy stay ends and the frame number location might be the least generic aspects here, but I'm not sure how much they can advance the i.d. search. One other thing that's somewhat interesting are those cable stops on the top tube. Normally, on frames I've seen, there are either no stops, they are on the underside of the top tube or the cables are routed internally. Unless, those were added later, which is always possible.
Too bad about the seat stay.