Can anyone give me any info on what type of late model suspension I can put into this sled to make it a little more "Back" friendly i.e. Polaris xtra 10,Cat........year and model of sled if possible. Thanks

if you replace your track with a 121 you could use almost any late model skid, if you use your track use a yamaha phaser skid,
(pre 90) they have a descent ride and are easy to come by.

The track is a 15x121 you can put a newer skid in them but it changes the ride alot and not really for the better since it ends up sitting real high in the back and low in the front

If you just replace the rear, you'll need to put some spacers in the front to bring it up, or it will bottom out all the time. Trust me....lol.
I put an sc10 in the back of an old massey ferguson, and it almost killed me until I raised the front a few inches. If you don't the approach angle for hitting any bumps on the trail, transfers all of that shock to the bars.
Happy sledding!!

Could maybe limit the rebound on the rear shock (internally) and pull in the limiter to match. Use softer springs and it may just work out. Don't try to get 10" of travel but rather 5-6", still much better than stock but without the "funny-car" look.