The bulge under the downtube socket of the bottom bracket is not that uncommon.
I have associated it with distortion during construction to get the inclusive angle where it is wanted.

The missing image for me is the seat lug without the seatpost binder bolt.
We can see it has been closed up, I would anticipate the correct seatpost size to be 26.4 or 26.6mm
I would also consider that the original derailleur hangar was sawed off. The dropouts look more Campagnolo than Simplex.

Frame could well have been for a particular client or bike shop. It has already been water-boarded as seen by the rust and not revealed the organization it worked for.