It's definitely a La Quelda model, and your date of 1948 could well be correct. These were nicely made frames and quite light too, as they were always made with good tubesets (531DB or Kromo). Sometimes they used an oversized top tube, especially in the larger sizes.
Would have been interested in buying it myself but it looks too small for me. I'm guessing it's about 22in or 23in.