I can get the complete xp suspension for just over a grand pretty big difference in price compared to a long travel kit.Not sure why you would bother? As you know, the rear trailing arm setup on the Polaris wouldn't be really easy to install on a Rhino without major fabrication work.
Unless you own a trashed (but suspension intact?) XP, there are MANY proven and reliable long travel setups that would be far superior to a stock XP suspension.
I think you'll spend more trying to make it work, than the cost of a good rhino long travel. To start there's not even a substantial frame structure below the seat to connect the trailing arm too.
Plus you'll probably need custom axles to adapt the inner rhino CVs to outer RZR CVs..