I bought a new SEI counter-rotation for my Stinger. It was a great price for what I thought was a very well-made product. You won't regret switching to CR. It was about 1400 bucks with gaskets and a complete new anode kit 2 years ago. You only need the lower unit, but I bought the whole drive because the price was so good and I would have all new parts. Although there have been some who complain about them (as with everything) I have about 50 hrs on mine and have had no issues. I bought mine straight off their website. They offer a three year fault-free warranty. When I'm done with my transom I'm going to order a new RH drive to match and keep my merc as a spare.
Biggus is right, you have to stick with Gen 1 if you have Gen 1. Also, if you didn't know, you have to swap the shift cable around and re-adjust the throw when you replace the outdrive. Not a big deal, but an important detail.
Link to their website---
http://www.sterndrive.cc/