It's been several years, but I looked into them and will relay what I know and what I can copy from available data:
Scorpion was a single seater, Scorpion II was a 2 seater.
Scorpion was the first offering from Rotorway, makers of the "Exec" series. Rotorway still offers some parts, but the aircraft is no longer "factory supported".
Scorpion became available in the late 60's.
The early models had very short life-limited parts - models after 1971 started addressing this somewhat.
The Scorpion II became available in 1972.
Earlier models had wood composite blades and an Evinrude 2-stroke engine. Later models, after 1974, featured a Rotorway manufactured engine - the RW133. If you must buy a Scorpion, these are the best to own as they have the most improvements.
All were AMATEUR BUILT, so be sure to inspect the helo very carefully. Being amateur built also means that you may find one that does not have the original type engine. I actually saw one with a Mazda 12A for power. (although I did not see it fly...)
Scorpion and Scorpion II were discontinued around 1980. The plans are now offered by a company called Vortech.
Believe it or not, the US Army planned a purchase of the original Scorpions as expendible scout helos. One even sits in the Fort Rucker museum.
I've also been told that one was used in a James Bond film.
Promo pic:
