Great bike! I have a real weakness for bikes of this vintage. Nice that it has the Atala branded Record hubs!
To your request for original build info I can supply a few guesses. Hopefully @
juvela and others more knowledgeable than myself will correct my errors:
Original brakes - Balilla, but maybe Universal 51.
Original handlebars - Ambrosio.
Original front derailleur - Grand Sport.
Original bottom bracket cable guide - Early Campag. with the cable housing stop for the front derailleur and the tubular guide for the rear derr.
Original seatpost - Campag. "small typeface" , but conceivably Unica-Nitor with Unica-Nitor seat.
Original saddle - Maybe Brooks B-17 Narrow. There were "Atala" branded saddles at one time but I know little about them.
Original bar plugs - REG. Gaslo are also period correct and super cool but expensive.
Period-correct and country-correct bottle cage - REG
Period correct and country-correct pump Silca non-framefit, preferably the early version with the rubber plug in the handle that allows for storage of a spare spoke or two inside.
Have fun,
Brent