That is a great bicycle -- thanks for sharing. The gearing reminds me of one of the stock offerings for the early 1960s Capo Sieger: 52-48 with a 14-22 5-speed Caimi freewheel in back. I am currently reassembling my Sieger with 49-45/14-28, if the Campag. GS can handle it, 14-26 if not.

The TA would, of course, be a period-correct crank, but have you looked into an early 1970s Campag. triple, which would look correct and give you 36T up front? I ran my Peugeot PKN-10 with a short-cage SunTour rear derailleur and 48-45-34 up front and 13-23 (6-speed) in back, and it was delightful. Your original derailleur set might be able to handle something similar. Even with your original freewheel, 36/22 is a very reasonable 44 gear-inches, comparable to the 42/26 low I have long used on my Bianchi and Peugeot.