Please keep in mind I am not an engine rebuilder or professional so take this info only as things I have found.
The pistons from the SeaDoo 580 engines are dual ring and I have used them in the 582 with good results.
I have used the single ring Piston with the caged bearings with some sucess (150 hrs ) no engine stoppage but never really felt comfortable flying behind the motor. I have been told, the dual ring piston dissappates heat better. The cageless bearing is said to provide better performance as well. I fly over prairie farmland so using a non stock parts may be more acceptable than if I was flying in the mountains. If you are looking for parts at a ski doo dealership tell them you are checking for a 1996 Grand touring 580. Most snowmo shops won't talk to you once you mention airplane. I sometimes use this site to check part numbers etc.
http://www.skidooparts1st.com/oempar...ring-580-parts
Good luck in your search
Norm