In 1978, Shimano introduced the Dura Ace EX series of parts. In it, Shimano introduced a lot of new concepts to their line. This included the introduction of the Shimano Uniglide cassette. While Shimano wasn't the first to introduce the cassette, they definitely made the concept popular, and stuck with the cassette concept for a number of years before it gained in popularity. Other little things they introduced in EX included one-key crank releases, standardization on all hex-key bolts, shaved teeth to improve shifting under load.
Also introduced was the UA-110 headset, better known in later years as the HP-7200. This headset is mostly known as the one with the funny wrench scallops.
While it doesn't require a special tool, a 32mm wrench isn't the greatest fit, and probably would result in marring the headset.
The HP-7200, and the closely related UB-110/HP-6200 differed only in their stampings, and in the use of an alloy crown race in the HP-7200. This resulted in a 44 gram weight difference. They were both available in parallel with an AX version, which was the same headset with a plastic fairing over the top assembly.
The Dura Ace and 600 EX headsets are often sold on eBay in conjuction with the word "rare". They were available from 1978 until 1984, so they're really quite common. Finding ones new-in-box, however, is a little less common.