Seller says it is aluminium after i asked" is it aluminium, or does a magnet stick to it". They might just be lazy, and assume it is because it doesn't weigh much, or they did do a magnet test. No way is it aluminium and that downtube is massive so combined with the top tube guides it must be light steel, or at a push a painted ti frame. Main triangle guides are all rivet jobs but seat stay is not which might be done to preserve the metal from another heat cycle, or the tubes are really thin. That or it was just a cool thing to do on a steel frame albeit it not normal.
Pics are taken through a sock, but i can make out some letters/numbers on the inside of each rear dropout. RH is something J56, i think, but cant make the other side out. Answers are short and sweet, form the seller, and i have no idea how he got 19" as a size. I asked how he measured and he just replied telling me the size is in the listing.
At the price it is worth a punt, to see what it is, if you can just right off 50 notes, but as he comes across as a rude and lazy car boot seller if there is anything wrong with it you will never find , out until you have it ,and then grief trying to sort it out. I can't imagine it would be packed well for the post. Just not getting the right vibes tbh.