And still no idea but doesn't look like the slot in the seat lug is TOO distorted so maybe the apparently too-small seat posts are not that far off, but I have no better idea from seeing these except would have a trusted shop with a sizing tool check the seat tube out (IF that was possible in the current lockdown in my town) and notice that the stays appear to be small diameter at th top("pencil stays" or are they "double tapered"?) which are a bit unusual for the apparent era, plus the "ears" have been filled which is a good touch and again something more seen on higher-end frames then ones built from lower grade/price tubing. One more thing (that would have been best to check when the tubes were not painted) but what are the Outer Diameters of all 3 main tubes, best to use a digital caliper or a dial caliper that shows metric fractions?
here's the shots for others to judge