Updated 11.20.2012

Universal (Italy) brakes were around pre-WWII. Not sure if they were making aluminum alloy versions pre-war (I have seen late-30s Bianchi with them, but don’t know if the alloy ones were put on the bike by the owner at a later date). There were #51 (alum. side-pull, early-50s), #61 (alum. center-pull, early-60s), #68 (alum. side-pull, mid-late-60s). The #61 was their response to the Mafac Racer center-pull, and the #68 was their answer to the Campagnolo side-pull.
Universal’s model designations correspond to the year of introduction. Universal top models were always considered “Pro-quality. “

Here’s an approximate time line on early models:

mod.35 – 1935 (side pull)
mod.39 – 1939 (side pull)
mod.50 – 1950 (side pull)
mod.51 – 1951 (side pull)
mod.61 – 1961 (center pull)
mod.68 – 1968 (side pull)

From Chuck Schmidt on the Classic Rendezvous mailing list:

Universal Dural calipers circa 1950s-60s.

photos courtesy Steven Maasland

Universal mod 61 center pull. A very popular "pro" bike brake in the 1960s.

Brake hoods for 61 & 68

Photo courtesy Scott Davis

Model SUPER 68

Gold anodized Super 68s

Super 77 brake set

Photo courtesy Kevin Kruger

Model CX circa early 1980s

Photo courtesy Hilary Stone

Model "Squadra"

LR-2 brake levers

Photo courtesy Kevin Kruger