I cannot tell if the front derailleur is mounted off a braze on or not.
English "ISO" threading, probably 130mm rear spacing.
Seatpost is probably a 27.2 but don't get a frame any larger and expect to use that aero seatpost. (in review, you may already have the post too low)
By the set up shown, not really much smaller either.

I would look for an Eddy Merckx or an American builder of the period. Will be def cheaper than a whole bike... well, maybe not, you have to look.
I found a terrific deal on an American builder made bike, complete for less than what I would have expected to pay for the frame alone a few years ago.
You may need a different length stem if you exchange frames, top tube lengths differ.
You could get an Italian frame, but most likely you will need to exchange the bottom bracket. The Italians held on with 36x24 threading, English, ISO is 1.370 x 24tpi with LH threading for the drive side.