Hi Wayne,
The 64 is the model number (nothing to do with a date if you were wondering). It's also known as the "Giro d'Italia". They were anodized, and had been around unchanged for a very long time... maybe since the 1960s
Other familiar alloy Cinelli bars:
#66 or "Campione del Mondo" It had a deeper drop and more rounded profile to the drops. Looking down from the top, it has very square corners before bending foward.
#65 or "Criterium" When viewed from the top these appears a lot more like Track racing bars with a more drastic foward bend.
That's pretty much everything I know about these handlebars. In their day, throughout the 70s-80s, they were about the best you could buy in an alloy bar. They were used by most of the Pro Teams. I know they were still being manufactured until at least around year 2000.
Originally, the bulge at the clamp area of Cinelli bars was 26.4mm - rather than 25.4mm (1 inch) like most others, or 26.0 like 3TTT (Italy). Some time in the 1990s Cinelli also began making them to fit 26.0 stems. 26.0mm had somehow eventually became the modern "standard" size for Road bar stem clamps in recent years... well... that is, until now with oversized carbon fiber bars and such.
Wayne, that's about all I know about the old Cinelli "classic" style bars. Hope its some use.
Cheers!
Bob Hanson, Albuquerque, New Mexico, USA