"AR 101.20.00322 originally corresponds to an Alfa Romeo Giulietta Sprint Speciale, manufactured on the 12th January 1961" and "the chassis number AR 101.20.00413 originally corresponds to an Alfa Romeo Giulietta Sprint Speciale, manufactured on the 9th March 1961"
I recieved this today from the owner of this chassis. Interesting to note the comparison of the two build dates. There is a difference of 91 cars between the two and a time line of about 84 calendar days. That could translate out to about a car a day. You can expect good quality at this level of production.
Just having some fun with numbers.