The calculator is subjective, don't consider it absolute. Put on an offset seatpost, 100-110 stem, and you'll probably be OK.
Italian bikes prior to 1960 typically had a top tube 2cm longer than the seat tube. Except when you got to the bigger frames. You get to 60cm, they are pretty much square.
Offset seat post and 110mm stem were part of that 70cm top tube recommendation 😂