All post 1973 Ruger single actions are New Models (note capitalization) and until 2005 all Blackhawks and Super Blackhawks were built on the same frame. Read on...
The original .357 Blackhawk was introduced in 1955. It featured a receiver size and grip frame (aluminum grip frame) close to that of the Colt SAA. They are now affectionately known as "flat-top" due to their perfectly flat topstrap. These were offered in 4 5/8", 6½", 7½" and 10" lengths. While they went through some design changes including the grip profile, topstrap configuration and ejector housing, they remained on the same Colt sized receiver and only 4 5/8" and 6½" barrels were available from 1962 until their discontinuation in 1972.
The original .44Mag Blackhawk, also known as "flat-top", was introduced in 1956. It featured the same grip frame as the .357 but with a larger receiver. These were available in the same lengths as the .357, except no 4 5/8". This gun went away in 1962 in favor of the Super.
The original Super Blackhawk was introduced in 1959 and featured the same "size" receiver as the earlier flat-top. It now had the "ears" on the topstrap, a different rear sight, a longer steel "Dragoon" grip frame and an unfluted cylinder. Only 7½" and 10" barrels were offered.
These original Blackhawks were also built in .30M1, .41Mag and .45Colt, all on the large frame.
In 1973 all the traditional guns, now called "Old Models", were discontinued in favor of a new design utilizing the transfer bar ignition and what would be termed "New Model" lockwork. Now all the Blackhawks are built on the same, identical large Super Blackhawk frame. Only the markings differ. These include .30M1, .32H&R/.32-20, .357/9mm, .38-40/10mm, .44Mag/.44-40 and .45Colt/.45ACP convertibles, the .357Mag, .41Mag, .44Mag and .45Colt. Then the Vaquero was also built on the large frame in various chamberings, only with fixed sights. This was true until 2005.
In 2005 Ruger introduced two new guns. The 50th anniversary .357 Blackhawk and the "New Vaquero" (in .357 and .45Colt). Both built on a smaller, mid-sized frame of the early .357's. Also with a new steel version of the old XR3 grip frame of the original 1955-1962 flat-tops.
Then in 2006 Ruger did a 50th anniversary of the .44Mag Blackhawk complete with flat-top frame, XR3 grip and 6½" barrel. They also did a special run of .41 Blackhawks based on this gun.
In 2009 they did a 50th Super Blackhawk with high polish bluing and some gold inlay.
Now there are mid-frame Blackhawks, based on the 50th .357 platform, chambered in .44Spl in 4 5/8" and 5½" lengths, blued and stainless, with XR3 and Bisley configurations. Some standard catalog items, some distributor exclusives.
The new 8-shot .327Federal is also on the large frame.