Ok, you mention way more durability and reliability then stock. And we know every 2 stroke can be improved on this , not just Polaris. Ski doo e tec design is not desirable in so many ways.
The snowmobile world has become a parts exchange program. You have a failure, just put on new parts. Or you have a failure and buy a so called kit and put it in and think it's better because they say so.
The problem with all of this is nothing is spec'd like tolerances , checking cylinder , ports, port heights,piston alloys, ring alloys, piston weight, etc.... I could go on ...
You want to build an engine that lasts then get a good performance shop like iantomassi to spec everything . Spec cylinder, port it, make sure pistons to cylinder are correct, get most out of air flow, install proper head design for fuel efficiency and hp, match valves to cylinder, port timing , both pistons weigh the same, etc,, basically blue printing above lower case . This is what will last , be reliable and have tons of hp too.
You can't just buy a kit , slap it in and think it's better for the reasons I explained above
Get a great reputable race shop like iantomassi to do your cylinder, get you pistons to match, head to match, etc... this is the proper way to do it .
Not the parts exchange program thing