Unless you have a wrecked sled right there to grab the parts off or they're dirt cheap, just grab a tki kit.
Belts for the tki are way cheaper, and the only one I've ever seen broken was from a stabbed track.
I've seen plenty of Polaris belts with the ribs ripped off, and mine has a tki because the stock upper pulley broke. It was a slight cost difference to buy the tki vs a stock belt and 2 pulleys.
Edit: looks like he doesn't have a chaincase version anymore. He used to have a 11-15 chain or 13-15 belt drive options. This would lead me to believe there's a difference. They both take different belts also.
May try calling, and see if it's possible to get a chaincase one ordered.